VAN  NOSTRAND  SCIENCE  JERI ES. 
.  jiff,  f.*rict;.&Q  Cents. 

SEWERAGE 

AND 

SEWAGE 
PURIFICATION 


BY  M.  N.  BAKER,  PH.  B.,  C.  E. 

ASSOCIATK  EDITOM,  *•  ENGINEERING  NEWS.'* 
JOINT  AUTHOK  u  SEWAGE  DISPOSAL  /.N  THE  UNITED  STATES.' 
AUTHOR  "SF.WAGE  PURIFICATION  IN  AMERICA," 
isH  SEV/A<;E  V.'ORKS." 


Fifth  Edition,  Revised  and  Enlarged. 

HBHT 

UC-NRLF 


157 

•  .    •• 

NEW  YORK: 

D,    VA]Nr  XOSTRAND   COMPANY, 
Park    Place. 
1913 


THE 


VAN  NOSTRAND 


Allan. 
No.  12.    THEORY  OF  VOUSSOIR  ARCHES.      By 

Prof.  Wm.  Cain.     Third  edition,  revised  and  enlarged. 


THE   VAN    NOSTRAND    SCIENCE    SERIES 

No.  13.     GASES  MET  WITH  "IN   COAL  MINES. 

By  J.  J.  Atkinson.  Third  edition,  revised  and  enlarged, 
to  which  is  added  The  Action  of  Coal  Dusts  by  Edward 
H.  Williams,  Jr. 

No.  14.    FRICTION  OF  AIR  IN  MINES.      By  J.  J. 

Atkinson.     Second  American  edition. 

No.  15.    SKEW  ARCHES.     By  Prof.  E.  W.  Hyde, 

C.E.     Illustrated.     Second  edition.    v 

No.  16.    GRAPHIC     METHOD     FOR     SOLVING 

Certain  Questions  iu  Arithmetic  or  Algebra.  By  Prof. 
G.  L.  Vose.  Third  edition. 

*No.  17.    WATER     AND     WATER-SUPPLY.      By 

Prof.  W.  H.  Corfield,  of  the  University  College,  London. 
Second  American  edition. 

No.  IS.    SEWERAGE     AND     SEWAGE     PURIFI- 

cation.  By  M.  N.  Baker,  Associate  Editor  "Engineer- 
ing News."  Fourth  edition,  revised  and  enlarged. 

No.  19.      STRENGTH       OF       BEAMS       UNDER 

Transverse  Loads.  By  Prof.  W.  Allan,  author  of 
"Theory  of  Arches."  Second  edition,  revised. 

No.  20.    BRIDGE  AND  TUNNEL  CENTRES.      By 

John  B.  McMaster,  C.E.     Second  edition. 

No.  21.    SAFETY   VALVES.     By  Richard  H.  Buel, 

C.E.     Third  edition. 

No.  22.    HIGH  MASONRY  DAMS.      By  E.  Sher- 
man Gould,  M.  Am.  Soc.  C.E.     Second  edition. 

No.  23.    THE    FATIGUE    OF    METALS    UNDER 

Repeated  Strains.  With  various  Tables  of  Results  and 
Experiments.  From  the  German  of  Prof.  Ludwig 
Spangenburg,  with  a  Preface  by  S.  H.  Shreve,  A.M. 

No.  24.  A  PRACTICAL  TREATISE  ON  THE 

Teeth  of  Wheel?.  By  Prof.  S.  W.  Robinson.  Third 
edition,  revised,  with  additions. 

No.  25.     THEORY      AND      CALCULATION      OF 

Cantilever  Bridges.     By  R.  M.  Wilcox.     • 

No.  26.  PRACTICAL  TREATISE  ON  THE  PROP- 

erties  of  Continuous  Bridges.     By  Charles  Bender,  C.E. 
No.  27.    BOILER  INCRUSTATION  AND  CORRO- 

aion.  By  F.  J.  Rowan.  New  edition.  Revised  and 
partly  rewritten  by  F.  E.  Idell. 

*No.  28.   TRANSMISSION  OF  POWER  BY  WIRE 

Ropes.     By  Albert  W.  Stahl,  U.S.N.     Fourth  edition, 
revised. 
No.  29.     STEAM  INJECTORS;  THEIR  THEORY 

and  Use.  Translated  from  the  French  by  M.  Leon 
Pochet. 


THE   VAN   NOSTRAND   SCIENCE  S  ERIES 

No.  30.    MAGNETISM  OF  IRON  VESSELS  AND 

Terrestrial  Magnetism.     By  Prof.  Fairman  Rogers. 

No.  31.    THE  SANITARY  CONDITION  OF  CITY 

and  Country  Dwelling-houses.      By  George  E.  Waring, 
Jr.     Third  edition,  revised. 

No.  32.    CABLE-MAKING     FOR     SUSPENSION 

Bridges.     B.  W.  Hildenbrand,  C.E. 

No.  33.    MECHANICS     OF    VENTILATION.      By 

George  W.  Rafter,  C.E.     Second  edition,  revised. 

No.  34.      FOUNDATIONS.          By       Prof.       Jules 

Gaudard,  C.E.     Translated  from  the  French.     Second 
edition. 

No.  35.  THE      ANEROID      BAROMETER;     ITS 

Construction  and  Use.  Compiled  by  George  W. 
Plympton.  Eleventh  edition,  revised  and  enlarged. 

No.  36.    MATTER    AND  MOTION.     By  J.  Clerk 

Maxwell,  M.A.     Second  American  edition. 

*No.  37.    GEOGRAPHICAL     SURVEYING;      ITS 

Uses,  Methods,  and  Results.  By  Frank  De  Yeaux 
Carpenter,  C.E. 

No.  38.    MAXIMUM     STRESSES     IN     FRAMED 

Bridges.  By  Prof.  William  Cain,  A.M.,  C.E.  New 
and  revised  edition. 

No.  39.    A     HANDBOOK     OF     THE     ELECTRO- 

Magnetic  Telegraph.  By  A.  E.  Loring.  Fourth  edi- 
tion, revised. 

*No.  40.       TRANSMISSION      OF     POWER     BY 

Compressed  Air.     By  Robert  Zahner,  M.E. 

No.  41.      STRENGTH        OF        MATERIALS.      By 

William  Kent,  C.E.,  Assoc.  Editor  "Engineering  News." 
Second  edition. 

No.  42.     THEORY        OF        STEEL  -  CONCRETE 

Arches,  and  of  Vaulted  Structures.  By  Prof.  Wm. 
Cain.  Fifth  edition,  thoroughly  revised. 

No.  43.    WAVE     AND     VORTEX    MOTION.     By 

Dr.  Thomas  Craig,  of  Johns  Hopkins  University. 

No.  44.     TURBINE       WHEELS.      By  Prof.  W.   P. 

Trowbridge,  Columbia  College.  Second  edition.  Re- 
vised. 

No.  45.     THERMODYNAMICS.     By    Prof.    C.    F. 

Hirshfeld.     Second  edition,  revised  and  corrected. 

No.  46.     ICE-MAKING      MACHINES.      From  the 

French  of  M.  Le  Doux.  Revised  by  Prof.  J.  E.  Donton, 
D.  S.  Jacobus,  and  A.  Riesenberger.  Sixth  edition, 
revised. 


SEWAGE  DISPOSAL 

IN  THE 

UNITED  STATES. 

BY 

GEO.  W.  RAFTER,  M.  Am.  Soc.  C.  E., 

AND 

M.   N.   BAKER,    Ph.B., 
ASSOCIATE  EDITOR  "ENGINEERING  NEWS." 


Large  Svo,  600  pages,  7  plates,  116  illustrations 
in  tJie  text. 


Part  I.  of  this  great  work  discusses  the  principles  of 
the  subject  in  detail,  citing  foreign  experience  where 
it  will  throw  light  upon  the  subject,  but  dealing  chiefly 
with  American  ideas  and  practice,  and  with  the  broad 
principles  of  sewage  purification,  or  other  means  of 
disposal,  which  are  more  or  less  applicable  every- 
where. Each  method  of  purification  is  discussed  at 
length,  and  many  allied  subjects  never  before  treated 
in  a  comprehensive  manner  are  taken  up. 

Part  II.  is  an  exhaustive  description  of  about  forty 
sewage  purification  plants  as  actually  built  in  the 
United  States  and  Canada,  with  many  details  of  cost, 
methods  of  operation  and  the  results  obtained  in  actual 
practice.  Several  appendices  give  English  and  Amer- 
ican Statute  Laws  regarding  stream  pollution  and  its 
prevention,  and  the  duties  and  powers  lodged  in  State 
Boards  of  Health  for  the  preservation  of  the  purity  of 
inland  waters,  especially  where  used  for  public  water 
supplies. 

SENT  POSTPAID  ON  KKCEIPT  OF  $6.00  BY  THE  PUB- 
LISHEBS, 

D.  VAN   NOSTRAND   CO., 
25  PARK  PLACE,  NEW  YORK  CITY. 


SEWERAGE 

AND 

SEWAGE 
PURIFICATION 


BY  M.  N.  BAKER,  PH.  B.,  C.  E. 

ASSOCIATE  EDITOR,  "ENGINEERING  NEWS." 

JOINT  AUTHOR  "SEWAGE  DISPOSAL  IN  THE  UNITED  STATES.'* 

AUTHOR  "SEWAGE  PURIFICATION  IN  AMERICA," 

"BRITISH  SEWAGE  WORKS." 


Fifth  Edition,  Revised  and  Enlarged. 


NEW  YORK: 
B,   VAN  NOSTRAND   COMPANY, 

.      ?5    Park    Place. 
1913 


COPTBIOHT,  1905, 

BY  D.  VAN  NOSTRAND  COMPANY. 
^IK  Rights  Reserved. 


PREFACE. 

One  of  the  earliest  volumes  in  this  series 
was  "  Sewerage  and  Sewage  Utilization,"  by 
Professor  W.  H.  Corfield,  of  the  Univer- 
sity of  London.  Appearing  in  1875,  when 
only  a  few  score  American  cities  had  sew- 
erage systems  worthy  the  name,  and  when 
sewage  purification  was  nractically  un- 
known in  this  country,  the  little  book  was 
and  for  many  years  continued  to  be  of  great 
service  this  side  the  water. 

When,  after  twenty  years,  the  publishers 
requested  the  author  to  revise  the  book,  he 
found  revision,  or  even  re-writirg,  entirely 
out  of  the  question,  so  ill-suited  were  its 
matter  and  method  to  modern  American 
conditions. 

There  being  a  strong  demand  for  a  brief 
but  comprehensive  book  on  the  subject,  it 
was  decided  that  an  entirely  new  one 
should  be  written. 

Professor  Corfield  entitled  his  discussion 


365610 


TV 


"  Sewerage  and  Sewage  Utilization."  The 
present  author  prefers  to  use  "  Purifica- 
tion," rather  than  "  Utilization,"  in  his 
title.  In  making  this  change  he  does  not 
wish  to  detract  from  the  importance  or 
possibilities  of  utilization,  but  simply  to 
put  purification,  or  the  sanitary  problem, 
first,  and  utilization,  or  the  commercial 
problem,  second.  In  addition,  utilization 
is  only  one  of  several  processes  of  purifi- 
cation. 

There  are  now  in  the  United  States  some 
fifty  cities  and  villages,  many  institutions, 
manufactories  and  houses,  employing  one 
or  another  system  of  sewage  purification. 
The  studies  of  the  Massachusetts  State 
Board  of  Health  have  given  an  impetus  to 
intermittent  filtration  of  late,  but  chemical 
precipitation  is  practiced  in  many  places 
and  broad  irrigation  is  quite  common,  es- 
pecially in  the  West,  where  "  Water  is 
King,"  and  the  sewage  is  used  for  plant 
drink  rather  than  plant  food. 

It  is  hoped  that  this  little  book  will  be 
of  use  to  some  engineers,  especially  those 
whose  practice  has  been  in  other  lines  of 


V. 


engineering,  and  to  that  vast  and  rapidly 
growing  body  of  sewer  commissioners  and 
superintendents,  boards  of  public  works, 
boards  of  health,  mayors  and  city  council- 
men,  and  public  spirited  citizen  in  general, 
all  of  whom  are  of  late  taking  a  growing 
and  most  promising  interest  in  sanitary 

problems. 

M.  N.  B. 

104  Tribune  Building, 

New  York,  Dec.  31, 1895. 


PREFACE  TO  THE  SECOND 
EDITION. 

In  the  nearly  ten  years  that  have  elapsed 
since  the  appearance  of  the  first  edition  of 
this  little  book,  the  newer  and  so-called 
bacterial  processes  of  sewage  treatment 
have  been  announced,  passed  through  an 
experimental  stage  and  come  into  extensive 
use.  Meanwhile  the  author  has  improved 
many  opportunities  to  visit  American  sew- 


VI. 


age  purification  works,  old  and  new,  and 
during  1904  spent  several  months  abroad, 
chiefly  in  Great  Britain,  visiting  sewage 
works  and  meeting  a  number  of  the  men 
prominently  connected  with  British  pro- 
gress in  this  field.  As  a  consequence  of 
the  events  named  above,  the  section  of  this 
book  which  deals  with  the  purification  of 
sewage  has  been  largely  rewritten  and 
somewhat  extended.  Few  changes  in  the 
other  section,  on  sewerage  systems  as  con- 
trasted with  disposal  works,  have  been 
deemed  necessary. 

M.  N.  B. 
220  Broadway, 

New  York,  May  5, 1905. 


CONTENTS. 

Page. 

Why  a  Sewerage  System  is  Needed 5 

The  Value  of  a  Sewerage  System 12 

Good  Engineering  Advice  Essential. 14 

Preliminary  Reports  and  Plans 15 

Separate  or  Combined  System 21 

Subsoil  Drainage 25 

Final  Disposal  of  Sewage 28 

Population,  Water  Consumption,  Volume  of 

Sewage,  Rainfall 34 

Method  of  Meeting  the  Cost 46 

Design    and    Construction   of  the    Conduit 

System 58 

Manholes 63 

Sewer  Grades 64 

Flushing  Devices 64 

Y-Branches  for  House  Connections 66 

Ventilation  of  Sewers 68 

Misapprehensions  Regarding  So-called  Sewer 

Gas 72 

Dr.  Billings'  Opinion  on  Sewer  Air  and  Ven- 
tilation   74 

Features  Peculiar  to  the  Combined  System..  77 

Oatch  Basins  or  Rainwater  Inlets 80 

Storm  Overflows 81 


vm. 

Page. 
Pumping  Stations,  Keceiving  Reservoirs  and 

Force  Mains 82 

Tidal  Chambers 84 

Final  Plans  and  Specifications .  8i 

Securing  Bids  and  Awarding  Contracts 86 

The  Proper  Lxecution  of  the  Contract 90 

Operating  the  System 92 

Sewarge  Commission,  Board  of  Public  Works 

or  City  Council 93 


Sewage  Purification  in  its  General  Aspects....  95 

Sedimentation 104 

Mechanical  Straining 106 

Chemical  Precipitation 108 

The  Septic  Tank 116 

Artificial  Aeration. — " Electrical"  Processes.  121 

Broad  Irrigation  or  Sewage  Farming 125 

Sub-Surface  Irrigation 131 

Intermittent  Filtration 131 

Contact  Beds 142 

Percolating  Filters 147 

Sewage  Purification  Plants  not  Nuisances 140 

The  Present  Status  of  Sewage  Purification....  150 


SEWERAGE    AND    SEWAGE    PURI- 
FICATION. 

WHY  A  SEWERAGE  SYSTEM  is  NEEDED. 


An  abundant  supply  of  pure  water  is 
one  of  the  greatest  advantages  which  any 
community  can  possess.  This  is  so  gener- 
ally recognized  that  every  American  town 
with  a  population  reaching  into  the  thous- 
ands has,  or  is  planning  to  obtain,  a  public 
water  supply.  Such  a  supply  having  been 
secured,  distributed  through  the  streets 
and  houses,  used  and  enjoyed,  what  dispo- 
sition shall  be  made  of  it  ?  Obviously  its 
removal  may  be  the  very  reverse  of  its  in- 
troduction. As  it  was'distributed  through 
a  network  of  conduits  diminishing  in  size 
with  their  ramifications,  so  it  may  be  col- 
lected again  by  similar  conduits,  increas- 
ing in  size,  as  one  after  another  they  unite 
in  a  common  outlet.  But  the  outgoing 
volume  is  far  different  from  the  incoming. 
The  influent  was  pure  and  limpid  ;  the 


effluent  has  been  fouled  in  performing  the 
services  demanded  of  it,  and  should  it  ac- 
cumulate and  remain  at  any  point  it 
would  decompose  and  give  rise  to  offensive 
odors.  Moreover,  in  its  various  fields  of 
usefulness,  the  once  pure  water  may  have 
taken  up  germs  of  disease  which  formerly 
habited  the  human  body,  causing  sickness 
and  perhaps  death,  and  which  might  give 
rise  to  like  dire  results  should  they  again 
secure  access  to  man.  What,  then,  shall 
be  done  with  the  fouled  water  that  has 
been  collected  ?  In  general,  there  are  but 
two  answers :  Either  it  must  (1)  be  turned 
into  a  body  of  water  so  large  as  to'dilute 
it  beyond  all  possibility  of  offence,  and 
where  it  cannot  endanger  human  life  by 
polluting  a  public  water  supply,  or  (2)  it 
must  in  some  manner  be  purified. 

This  fouled  water  is  called  sewage;  the 
conduits  which  collect  it  constitute  the 
sewerage  system ;  and  the  means  adopted 
to  get  rid  of  the  collected  matter  is  termed 
sewage  disposal.  The  terms  sewerage  and 
sewage,  it  may  be  noted  here,  are  often 
confounded,  even  among  engineers.  The 


use  of  sewerage  to  indicate  the  matter  car- 
ried by  a  sewer,  is  obsolete,  so  that  one 
might  about  as  properly  write  or  speak  of 
purifying  water- works  as  of  purifying 
sewerage. 

To  go  a  little  further  with  definitions, 
it  may  be  stated  that  conduits  which  cany 
water  collected  from  street  surfaces,  dur- 
ing and  after  rains,  or  ground  water  col- 
lected from  beneath  the  surface,  or  both, 
are  called  drains.  Where  one  set  of  con- 
duits removes  sewage  and  another  carries 
surface  and  ground  water,  it  is  said  that 
the  separate  system  of  sewerage  is  in  use, 
a  term  which  may  be  applied  where  the 
drainage  system  has  not  yet  been  con- 
structed, but  only  sanitary  sewers,  as  they 
are  often  called,  have  been  provided. 
Where  one  set  of  conduits  conveys  both 
sewage  and  drainage  water,  it  is  called  the 
combined  system  of  sewerage.  Obviously, 
various  modifications  of  those  two  systems 
are  possible,  both  for  whole  cities  and  for 
limited  areas  within  one  municipality. 

To  make  the  distinction  between  sewers 
and  drains  more  complete,  it  may  be  said 


s 


that  sewers  carry  water  fouled  with  or- 
ganic wastes  from  the  human  system,  from 
various  cleansing  processes  common  to 
all  households,  and  also  manufacturing 
wastes;  while  drains  convey  rain  or  ground 
water  only.  The  drainage,  however,  may 
contain  much  organic  matter  gathered  by 
the  rain  in  passing  over  roofs,  yards  and 
streets,  or  by  the  ground  water  as  it  per- 
colates through  polluted  soil;  but  this 
matter,  in  most  cases,  is  far  less  likely  to 
give  offense  or  menace  health  than  that 
contained  in  sewage. 

Before  entering  into  a  discussion  of 
sewerage  systems  it  will  be  well  to  con- 
sider briefly  why  they  are  needed,  for  the 
engineer  and  the  sanitarian  must  for  many 
years  to  come  meet  the  objections  to  this 
class  of  improvements  put  forth  by  men 
either  ignorant  of  the  principles  involved 
or,  worse  yet>  of  those  whose  first  impulse 
is  to  strenuously  resist  any  new  demand 
upon  the  public  treasury,  without  regard 
to  its  character. 

Public  water  supplies  and  sewerage 
systems  naturally  go  hand  in  hand.  Where 


neither  exists  water  is  generally  drawn 
from  wells,  often  in  close  proximity  to 
privies  and  sink  drains,  and  subject  to 
gross  pollution  from  them.  Should  there 
be  a  case  of  typhoid  fever  in  a  given  house 
typhoid  germs,  which  always  exist  in  great 
numbers  in  the  dejecta  of  the  patient, 
might  readily  find  their  way  into  the 
well,  and  thus  into  the  digestive  system  of 
other  members  of  the  family,  of  visitors, 
or  of  neighbors  using  the  well.  Thus  the 
disease  is  spread  from  one  member  of  a 
family  to  another  and  from  family  to 
family.  Besides  this  danger,  there  is 
always  the  more  remote  one  from  the 
dreaded  cholera,  should  it  visit  the  country, 
and  the  ever  present  one  of  poor  health 
and  consequent  greater  susceptibility  to 
all  forms  of  disease. 

A  sanitary  sewerage  system  cannot  be 
installed  until  a  public  water  supply  has 
been  provided.  It  is  needed  as  soon  as 
that  is  accomplished,  for  while  the  wells 
can  then  be  abandoned  the  volume  of 
waste  water  is  greatly  augmented  by  the 
water-works  system.  Its  foulness  is  also 


10 

greatly  increased  through  the  introduc- 
tion of  water  closets.  Without  sewers  and 
with  a  public  water  supply  cesspools  must 
be  employed.  With  cesspools  begins  a 
continuous  and  far-reaching  pollution  of 
the  soil,  much  more  serious  than  that 
which  commonly  results  from  privies 
and  the  surface  disposal  of  slops.  The 
pores  of  the  ground  become  clogged 
with  organic  waste;  nature's  beneficent 
process  of  oxidation  is  arrested ;  putrefac- 
tion sets  in ;  and  poisonous  gases  are  gene- 
rated. These  gases  may  find  their  way 
through  foundations  into  houses  and  also 
directly  into  the  outer  air,  especially  dur- 
ing sudden  rises  in  the  ground  watrr  level. 
The  cellars  of  houses  on  small  lots  may 
be  made  damp  by  leaching  cesspools. 
Such  wells  as  still  remain  in  use  are  also 
liable  to  pollution  from  cesspools  on  neigh- 
boring premises.  Water  tight  cesspools, 
while  possible  in  theory  and  often  de- 
manded by  health  ordinances,  are  a  luxury 
that  only  a  few  can  afford,  owing  to  the 
cost  of  frequent  emptyings.  Even  in  per- 
meable 'soils  the  emptying  of  leaching 


11 


cesspools  as  often  as  health  and  decency 
demand  will  generally  cost  more  than  the 
increase  in  taxes  due  to  the  construction 
and  maintenance  of  a  sewerage  system. 

A  village  or  town  without  water-works 
and  sewers  is  at  great  disadvantage  as 
compared  with  communities  having  these 
conveniences  and  safeguards.  Industries 
and  population  are  not  so  quickly  attracted 
to  it;  the  health  of  the  municipality  is 
almost  sure  to  be  poorer  and  its  death  rate 
higher.  These  statements  hold,  only  in 
lesser  degree,  where  a  public  water  sup- 
ply but  no  sewerage  system  has  been  pro- 
vided. The  full  benefits  of  water-works 
cannot  be  enjoyed  until  sewers  are  put  in, 
because  many  people  will  make  the  ab- 
sence of  sewers  an  excuse  for  the  non-use 
or  limited  use  of  the  water  supply. 

Who  can  describe  the  trials  and  tribula- 
tions which  beset  health  authorities  in 
their  efforts  to  secure  the  proper  disposal 
of  privy  and  cesspool  matter  ?  If  there  is 
little  but  privy  matter  to  be  removed  the 
difficulties  are  not  so  great,  because  in  this 
country  such  a  condition  seldom  exists, 


12 

except  in  small  communities,  where  the 
houses  are  set  in  ample  lots,  with  gardens, 
and  with  an  abundance  of  farm  land  near 
by,  so  that  the  vault  matter  is  in  demand 
for  fertilizing  purposes.  With  denser 
populations  and  larger  areas,  the  emptying 
of  vaults  is  a  more  serious  matter,  requir- 
ing the  greatest  care  to  prevent  nuisances, 
and  often,  if  not  generally,  entailing  ex- 
pense upon  the  householder.  Cesspools 
are  unmitigated  nuisances,  and  however 
well  built  or  frequently  emptied,  the  satis- 
factory disposal  of  their  contents  is  practi- 
cally impossible.  The  matter  has  com- 
paratively little  value  as  a  fertilizer  and 
dumping  upon  unoccupied  land  is  met  with 
increasing  protests,  even  if  the  land  is 
located  in  remote  and  sparsely  settled 
towns. 

THE  VALUE  OF  A  SEWERAGE  SYSTEM. 

To  express  the  value  of  a  good  sewerage 
system  in  lives  or  dollars  saved  is  simply 
impossible.  Other  sanitary  improvements 
precede,  accompany  and  follow  this,  each 


13 

adding  to  the  healthfullness  of  the  com- 
munity. The  decrease  in  the  death  rate 
for  a  term  of  years  can  be  given,  but  no 
man  can  express  in  percentages  the  part 
played  by  each  factor.  We  know  that 
pure  air,  pure  water,  and  a  pure  soil  are 
essential  to  good  health  and  long  life. 
Among  the  greatest  polluters  of  air  and 
soil,  and  by  all  odds  the  greatest  enemy  to 
pure  water,  is  the  contaminating  matter 
from  privies,  cesspools  and  improper  sys- 
tems of  sewerage  and  sewage  disposal. 
These  are  such  truisms  that  to  expand 
upon  them  in  these  days  of  progress  seems 
almost  absurd. 

Only  one  illustration  will  be  attempted. 
More  than  35,000  deaths  a  year  are  caused 
by  typhoid  fever  in  the  United  States. 
Keep  from  the  lips  of  our  people  all  water 
containing  germs  from  the  excreta  of  ty- 
phoid patients,  and  milk  diluted  with 
such  water,  or  contaminated  with  it 
through  washing  milk  cans  and  bottles 
in  it,  and  the  disease  would  soon  be  prac- 
tically wiped  out.  This  can  be  effected 
only  by  providing  every  one  with  a  pure 


14 


water  supply,  which,  with  other  much  de- 
sired ends,  would  be  greatly  advanced  by 
the  provision  of  properly  designed  sewer- 
age and  sewage  disposal  systems  for  both 
town  and  country.* 

GOOD  ENGINEERING  ADVICE  ESSENTIAL. 

Simple  and  convincing  as  the  arguments 
for  efficient  sewerage  systems  seem,  years 
of  agitation  are  often  necessary  to  awaken 
sufficient  interest  in  the  subject  to  secure 
their  introduction.  One  cause  of  this  is 
the  failure  to  present  to  the  people  a  well- 
considered  scheme,  capable  of  beingunder- 
stood  in  its  broad  outlines  by  the  average 
citizen  and  in  all  but  its  most  technical 
details  by  any  live  business  or  professional 
man.  How  rarely  this  is  done  until  years 
have  been  spent  in  well  nigh  useless  effort, 
money  as  well  as  time  often  being  wasted 


*  For  the  salutary  effect  upon  the  general  health  of 
individuals,  and  especially  of  women,  conferred  by  the 
abolition  of  outside  privies,  more  or  less  exposed  to  the 
public  view,  cold  in  winter,  insufferably  hot  and  odorous 
in  summtr,  impossible  of  access  without  getting  wet  dur- 
ing rains  or  snows,  see  Waring's  "  How  to  Drain  a 
House,"  Second  Edition.  This  book  discusses  other  bene- 
fits to  health  and  otherwise,  conferred  by  a  proper  system 
of  disposal  for  household  wastes  of  the  kind  under  discussion 
here. 


15 


in  this  way.  Good  engineering  advice  is 
needed  from  the  very  start  in  this  or  any 
similar  enterprise.  Otherwise  a  chaotic 
mass  of  opinions  as  to  what  should  be 
done  speedily  develops,  factions  spring  up 
and  even  political  parties  take  sides  on  the 
questions  involved. 

PRELIMINARY  REPORTS  AND  PLANS. 

Such  preliminary  studies  as  are  required 
need  not  be  very  expensive,  but  they  are 
essential  to  a  proper  understanding  of  the 
subject.  Among  the  data  which  should  be 
determined  as  early  as  possible  are:  (1) 
The  area  to  be  served,  with  its  topography 
and  the  general  character  of  the  soil.  (2) 
Whether  the  separate  or  combined  system 
of  sewerage,  or  a  compromise  between 
these  two,  is  to  be  adopted.  (3)  Whether 
subsoil  drainage  shall  be  attempted.  (4) 
The  best  of  the  available  means  of  final 
disposal  of  the  sewage,  often  the  most 
difficult  of  the  problems  involved  where 
purification  is  necessary.  (5)  Population, 
water  consumption  and  volume  of  sewage 
for  which  provision  must  be  made,  together 


16 

with  rainfall  data,  if  surface  drainage  is  to 
be  installed.  (6)  Extent  and  cost  of  the 
proposed  system.  (7)  Method  of  meeting 
the  cost  of  the  sewerage  system.  (8)  The 
needs  for  sewerage  peculiar  to  the  locality, 
with  a  study  of  the  health  and  mortality 
of  the  town. 

These  are  the  main  points  involved  in 
sewering  and  draining  a  town.  It  may 
serve  either  as  a  mere  outline,  or  the  de- 
tails suggested  by  the  various  heads  may 
be  so  worked  out  as  to  form  a  complete 
design  for  the  system. 

There  is  nothing  like  public  confidence, 
and  the  quickest  way  to  unsettle  a  com- 
munity and  to  delay  the  introduction  of 
public  improvements,  is  to  lay  before  the 
people  a  number  of  conflicting  plans.  A 
well-considered  preliminary  study  is  likely 
to  at  once  commend  itself  to  citizens  and 
taxpayers,  and  if  months  or  even  years  go 
by  without  further  action  it  continues  to 
be  a  rock  upon  which  to  build  in  the  future. 
Succeeding  engineers  can  but  commend 
what  has  been  so  well  put  in  the  past,  if 
they  be  possessed  of  sense  and  ability,  and 


17 

the  popular  conception  of  what  should  be 
done  is  strengthened  with  each  endorse- 
ment of  previous  recommendations. 

The  above  being  true,  great  care  should 
be  taken  on  the  part  of  local  authorities  to 
select  the  right  man  for  the  preliminary 
studies,  and  the  fortunate  engineer  should 
exercise  even  greater  care  in  fulfilling  the 
trust  confided  in  him.  The  same  holds 
good  regarding  final  plans  and  actual 
construction. 

Generally  speaking,  the  smaller  the  com- 
munity or  the  amount  of  money  available, 
the  greater  the  need  for  the  best  obtain- 
able advice,  although  of  course  the  less 
intricate  the  problem  the  cheaper  its  solu- 
tion, even  by  the  most  talented  expert.  It 
is  only  a  false  economy  that  dispenses 
with  engineering  services,  or  employs  the 
cheapest,  because  money  is  to  be  had  only 
in  small  quantities.  Experience  is  an  ex- 
pensive teacher,  and  the  community  that 
realizes  this  at  the  start  will  pay  the  engi- 
neer and  secure  the  benefit  of  his  training 
in  the  school  of  well-directed  experience, 
instead  of  taking  a  more  expensive  course 


18 


of  its  own  in  the  school  of  headstrong, 
blundering,  haphazard  experience,  which 
so  many  municipalities  have  entered. 

Let  us  now  suppose  that  a  village,  town, 
or  city  has  so  far  decided  in  favor  of  a 
sewerage  system  as  to  be  ready  to  have 
preliminary  studies  made.  We  will  also 
suppose  that  it  has  decided  to  have  these 
studies  of  a  comprehensive  character.  The 
authorities  hesitate  somewhat  between  em- 
ploying a  local  engineer  of  good  general 
standing  in  his  profession,  and  with  some 
experience  in  sewerage  construction,  and 
an  engineer  of  national  reputation  in  this 
line  of  work.  Wishing  the  best  they 
half  decide  to  engage  the  latter,  but  in- 
quiry develops  the  fact  that  his  charges 
are  high,  although  none  too  high  con- 
sidering his  experience  and  knowledge, 
that  he  must  be  paid  for  time  spent  in 
travelling,  and  that  a  comparatively  large 
amount  of  ordinary  surveying  and  simple 
compilation  of  facts  and  figures  must  be 
made,  requiring  a  number  of  days  from  a 
principal  arid  assistants.  Both  the  local 
man  and  the  expert  are  finally  engaged, 


19 


the  latter  to  act  principally  in  an  advisory 
eapaeity  throughout  the  study. 

Referring  to  the  above  outline  for  the 
preliminary  study,  it  will  be  seen  that  the 
local  engineer  will  make  the  surveys,  collect 
the  information  regarding  population, 
water  consumption  and  rainfall  and  other 
merely  local  data  upon  which  the  design 
for  a  sewerage  system  will  depend.  This 
he  will  submit  to  the  expert  for  use  in 
preparing  the  report  of  the  latter.  It  is 
not  necessary  to  separate  any  further  the 
work  of  the  two  engineers.  The  evolution 
of  the  report  and  recommendations  may 
therefore  be  considered  as  the  work  of  one 
engineer  from  start  to  finish.  Indeed  it  is 
likely  to  be  so  to  a  very  large  extent  in  prac- 
tice, the  division  of  labor  generally  being 
carried  far  to  one  extreme  or  the  other: 
That  is,  either  the  expert  is  called  in  to 
amend  and  approve  the  results  of  complete 
studies  by  an  engineer  with  less  experience 
than  himself,  or  he  employs  his  own  as- 
sistants, local  engineers  or  otherwise,  to 
do  the  bulk  of  the  routine  work  involved. 


20 

The  various  parts  of  the  study  in  their 
order  may  now  be  taken  up,  as  follows: 

(1)  The  area  to  be  served,  with  its  topog- 
raphy and  the  general  character  of  the  soil. 

A  contour  map  of  the  whole  municipality, 
showing  the  location  of  the  several  streets, 
streams,  ponds,  or  lakes  and  contour  lines 
for  say  each  5  ft.  of  change  in  elevation 
is  essential  to  the  best  results  and  must  be 
provided  sooner  or  later  if  a  sewerage 
system  is  to  be  carried  out  on  intelligent 
lines.  Such  a  map  will  be  of  service  for 
other  purposes  and  would  be  a  good  invest- 
ment for  any  municipality. 

The  general  character  of  the  soil  can 
usually  be  ascertained  without  much  diffi- 
culty by  more  or  less  casual  observation, 
and  by  inquiring  among  residents,  build- 
ers and  others  who  have  dug  wells  and 
cellars,  or  observed  the  same  while  being 
dug.  The  kind  of  soil  is  important  as 
affecting  the  cost  of  trenching,  and  its 
natural  wetness  or  drynoss,  together  with 
the  ground  water  level,  will  be  a  further 
indication  of  the  difficulties  likely  to  be 
met  in  construction,  and  of  the  necessity 


21 

or  desirability  of  providing  underdrains 
for  removing  ground  water  or  lowering  its 
level,  which  is  further  considered  below. 

(2)  Whether  the  separate  or  combined 
system  of  sewerage,  or  a  compromise  be- 
tween these  two,  is  to  be  adopted. 

Obviously,  these  points  depend  almost 
wholly  upon  local  conditions,  including 
financial  as  well  as  natural  factors.  The 
size  and  cost  of  combined  sewers  is  truly 
enormous  as  compared  with  those  on  the 
separate  plan,  since  the  surface  drainage 
in  times  of  heavy  rainfall  is  many  times 
as  great  as  the  flow  of  sanitary  sewage. 

In  the  older  towns  and  cities  it  is  some- 
times the  case  that  drains  designed  to  re- 
move only  surface  water  were  con- 
structed long  ago,  before  modern  plumb- 
ing methods  were  introduced.  Such  drains 
were  loosely  built,  may  have  been  poor  in 
grade  from  the  start  and  were  never  de- 
signed to  receive  sewage.  To-day,  how- 
ever, they  are  serving  as  sewers  and  giv- 
ing much  trouble  and  offense  through 
stoppages  and  stagnation.  Besides  this, 
they  are  polluting  the  soil  by  means  of 


numerous  leaks.  In  designing  a  compre- 
hensive sewerage  system  for  such  a  city,  it 
sometimes  happens  that  these  old  drains 
can  be  relegated  to  their  original  purposes 
and  sanitary  sewers  introduced  to  care  for 
house  wastes  alone. 

Where  a  town  or  city  is  entirely  or  prac- 
tically without  either  sewers  or  drains,  it 
often  happens  that  it  may  consider  itself 
fortunate  if  it  can  put  in  sanitary  sewers 
on  the  strictly  separate  plan,  leaving  sur- 
face drainage  for  future  generations,  it 
may  be.  Here  financial  limitations  govern, 
and  this  has  been  the  experience  of  many 
American  municipalities  now  possessed 
of  first-class  sanitary  sewers. 

Many  a  town  is  so  situated  that  street 
gutters  and  natural  water  courses  alone 
make  ample  provision  for  surface  drainage. 
Again,  the  street  gutters  may  be  insuffi- 
cient, through  various  causes,  and  storm 
drains  thus  be  necessary,  but  there  may  be 
numerous  natural  outlets  for  these  at  fre- 
quent intervals,  thus  requiring  only  short 
lines  and  thus  comparatively  small  storm 
drains.  At  the  same  time  the  only  suita- 


23 

ble  outlet  for  sewage  may  be  at  a  point 
remote  from  the  city,  thus  necessitating  a 
long,  large  and  costly  outlet  sewer,  if  the 
combined  system  were  to  be  employed,  as 
against  a  comparatively  small  and  inex- 
pensive outlet  for  sewage  alone. 

But  strongest  of  all  is  the  case  for  the 
separate  system  when  the  sewage  must  be 
purified.  It  is  simply  out  of  the  question 
for  any  city  to  build  works  large  enough 
to  treat  the  full  flow  of  a  combined  system 
at  times  of  maximum  rainfall.  Some  of 
the  sewage  must  pass  away  entirely  un- 
treated, or  very  inadequately  purified. 
Generally  speaking,  each  added  drop  of 
water  is  so  much  more  burden,  for  while  it 
is  true  that  the  sewage  is  thereby  diluted, 
it  is  also  true  that  the  capacity  of  the  works 
is  taxed  so  much  the  more. 

If  crops  are  being  raised,  or  even  simple 
intermittent  filtration  is  in  vogue,  periods 
of  heavy  rainfall  are  just  the  times  when 
a  smaller  rather  than  a  larger  volume  of 
sewage  ig  desired,  while  at  chemical  precipi- 
tation works  heavy  increases  in  the  sewage 
flow  are  always  unwelcome.  The  volume 


to  be  treated  is  one  of  the  greatest  factors 
in  sewage  purification,  and  the  original 
size  of  .a  plant,  and  largely  its  cost,  vary 
directly  with  the  volume,  while  cost  of 
operation  is  far  more  largely  dependent 
upon  volume  than  strength  of  sewage. 
The  essential  point  is,  that  the  combined 
system  means  great  extremes  and  sudden 
fluctuations  of  flow,  and  whatever  the 
character  of  the  industry  such  conditions 
are  consistent  neither  with  economy  nor 
the  best  results. 

Sometimes  more  or  less  limited  areas  of 
a  town  may  require  the  combined  system 
through  lack  of  facilities  for  near-by  dis- 
posal of  surface  water,  and  again  roof 
water  alone  may  need  to  be  taken  into  the 
sewers.  As  stated  above,  local  conditions 
and  relative  costs  are  the  governing  fac- 
tors in  deciding  between  the  separate  and 
combined  systems. 

An  old  fallacy  concerning  the  combined 
system  may  be  mentioned,  although  it  has 
now  well  nigh  disappeared:  It  is  that  the 
storm  water  will  flush  the  sewers.  Regard- 
ing this  it  must  be  remembered  that  the 


25 

sewage  flow  is  continuous  and  likewise  the 
dangers  of  and  from  stoppages,  while  rain- 
falls are  uncertain  in  frequency  and 
amount.  As  a  matter  of  fact  special  pains 
are  now  taken  by  the  best  engineers  to  give 
combined  sewers  such  a  section  that  the 
dry  weather  flow  will  be  in  a  small  chan- 
nel as  much  as  possible  like  that  which 
might  be  employed  for  sanitary  sewers.* 

(3)  Whether  subsoil  drainage  shall  be 
attempted. 

As  for  providing  underdrains  for  remov- 
ing ground  water,  this  will  also  in  most 
cases  depend  upon  local  conditions.  It  is 
always  an  advantage  to  lower  the  ground 
water  level  in  places  where  it  is  high  enough 
to  render  the  ground  wet  at  or  near  the  sur- 
face through  a  large  part  of  the  year.  As 
sewers  are  generally  placed  below  the  level 
of  cellar  bottoms  and  underdrains  are  most 
commonly  put  below  or  at  least  not  higher 
than  the  sewers,  it  follows  that  when  of 
ample  size  underdrains  will  lower  the 


loiv  i-; 


i-xtended  discussions  01'  the  combined  and  separate 
systems  may  be  found  in  Waring s  "Sewerage  and  L  :nd 
Dra.nage,"  Staley  &  Pierson's  "  Separate  System  of  Sewer- 
age," and  the  many  reports  of  engineers  on  proposed  sew- 
erage systems. 


ground  water  level  to  a  considerable  depth 
below  the  surface  and  render  house  foun- 
dations practically  dry.  It  may  be  neces- 
sary to  supplement  the  street  underdrains 
by  branches  running  to  the  houses,  and 
even  extending  through  large  lots. 

The  advantage  of  rendering  dry  the  soil 
beneath  and  around  habitations  need  nut 
be  enlarged  upon  here,  as  it  is  so  generally 
well  known.  But  it  may  not  be  known  to 
all  that  underdrains  are  often  such  great 
aids  to  good  sewer  construction  as  to  war- 
rant their  introduction  for  the  benefits 
caused  during  construction  alone.  This  is 
the  case  where  the  trenches  are  so  wet  as 
to  render  the  making  and  setting  of  cement 
joints  difficult.  By  putting  in  underdrains 
iii  advance  of  the  sewer  proper  the  trench 
may  be  kept  dry  and  the  work  greatly 
facilitated,  even  where  temporary  pumps 
must  be  provided  to  remove  the  water  col- 
lected. 

Where  it  is  desirable  for  any  reason  to 
keep  down  the  sewage  flow  to  the  lowest 
possible  point,  underdraius  are  also  of 
value  without  regard  to  sanitary  condi- 


27 

tions.  This  may  be  the  case  where  the 
sewage  is  to  be  purified,  or  simply  to  be 
pumped,  or  where  several  municipalities 
use  a  joint  outlet  sewer,  each  contributing 
towards  the  maintenance  of  the  outlet  in 
proportion  to  the  amount  of  sewage  from 
its  individual  system.  The  latter  condi- 
tions are  found  in  a  joint  outlet  in  New 
Jersey,  where  Orange,  Bloomfield  and 
Montclair  use  the  same  trunk  sewer  to 
the  Passaic  River,  and  have  as  the  only 
basis  of  dividing  the  cost  of  maintenance 
the  amount  of  sewage  contributed  by  each. 

Of  course  the  aim  in  good  sewer  work  is 
to  reduce  the  infiltration  of  ground  water 
to  a  minimum,  but  all  engineers  and  con- 
tractors know  that  in  very  wet  soils  tight 
joints  can  be  made  only  with  difficulty  and 
practically  never  with  absolute  certainty. 
The  volume  of  flow  in  the  outlet  of  the 
sanitary  sewers  at  East  Orange,  N.  J.,  was 
at  one  time  fully  half  ground  water,  ac- 
cording to  careful  estimates,  and  that  was 
after  the  sewerage  system  was  well  estab- 
lished. 

It  must  be  remembered  that   with   the 


28 

2-ft.  lengths  of  vitrified  sewer  pipe  now 
almost  universally  used,  there  are  2,640 
joints  to  the  mile.  These  joints  are  made 
of  cement,  and  are  not  for  a  moment  com- 
parable with  the  joints  of  molten  lead,  with 
their  subsequent  heavy  calking,  used  in 
water  main  construction. 

In  view  of  the  above  it  is  evident  that 
underdrains  should  be  used  where  they 
may  be  expected  to  benefit  the  health  of  a 
community  by  lowering  the  ground  water 
level;  where  they  will  be  sufficient  aids  to 
sewer  construction  to  warrant  their  intro- 
duction for  this  purpose,  to  which  is  also  to 
be  added  their  permanent  benefit;  and 
finally,  where  it  is  desirable  to  employ  them 
to  prevent  an  increase  through  infiltration 
of  the  volume  carried  by  the  sewage,  in 
which  case  the  benefit  to  health  will  also 
accrue. 

(4)  The  best  of  the  available  means  for 
the  final  disposal  of  the  sewage. 

Until  recently  this  part  of  the  problem,  at 
least  in  America,  meant  only  into  which  of 
the  near-by  streams  or  lakes  or  at  what 
point  in  tide  water  could  the  crude  sewage 


be  discharged  at  the  least  cost  and  with  the 
minimum  of  offence.  Too  often  the  matter 
of  offence  was  given  only  scant  consider- 
ation, and  sometimes  none  at  all.  Un- 
fortunately many  cities  are  to-day  facing 
the  problem  in  the  same  manner,  but  the 
advance  of  modern  sanitation  is  rendering 
this  more  and  more  imposible. 

The  cardinal  principle  in  the  ultimate 
disposal  of  sewage  is  that  no  public  water 
supply  should  be  endangered  thereby. 
Strange  to  say,  this  must  be  interpreted  as 
meaning  that  no  city  should  endanger  the 
water  supply  of  either  itself  or  its  neighbors. 
This  is  almost  inconceivable,  for  while  one 
can  imagine  a  city  mean  or  ignorant  enough 
to  endanger  the  lives  of  the  citizens  of  an 
adjoining  community,  it  seems  incredible 
that  any  municipality  should  be  sufficiently 
reckless  to  poison  its  water  supply  with  its 
own  excreta.  But  both  conditions  exist  and 
must  be  combated.  This  deplorable  state 
of  affairs  may  be  explained  in  part  by  the 
general  ignorance  of  sanitary  matters 
which  has  prevailed  until  of  late,  and  in 
fact  is  seen  still  to  exist  when  one  com- 


pares  what  is  with  what  should  l»e.  It 
does  seem,  though,  that  common  sense  and 
common  decency  combined  ought  to  be 
sufficient  to  prevent  a  city  from  drinking 
its  own  sewage  or  forcing  it  down  the 
throats  of  others. 

Coming  back  to  the  cardinal  principle 
expressed  above3  it  may  be  asked  "what 
constitutes  the  endangering  of  a  public 
water  supply?"  No  very  definite  answer 
can  be  given  at  present,  owing  to  our  lack 
of  knowledge  regarding  the  exact  length 
of  time  which  disease  germs  from  the 
human  system  will  live  in  water.  The 
Massachusetts  legislature  some  time  ago 
said  that  no  excreta  should  be  discharged 
into  a  stream  within  20  miles  of  any 
point  where  it  is  used  for  a  public  water 
supply,  but  in  the  matter  of  new  water 
and  sewerage  construction  it  has  practi- 
cally placed  the  subject  in  the  hands  of 
its  State  Board  of  Health.  There  are  no 
data  to-day  which  will  warrant  an  engin- 
eer in  saying  that  disease  germs  may  not 
be  conveyed  more  than  20  in;les  by  the 
waters  of  a  stream  and  afterwards  cause 


31 

sickness  and  perhaps  death.  The  engineer 
and  sanitarian  will  consider  the  distance 
which  must  be  traversed  by  the  sewage 
and  the  dilution  which  it  would  receive 
before  reaching  a  public  water  supply,  to- 
gether with  the  minimum  length  of  time 
which  would  elapse  before  a  disease  germ 
could  pass  from  one  human  system  to 
another,  a  most  important  point.  Unless 
distance,  dilution,  and  time  are  great,  sew- 
age should  be  purified  or  carried  elsewhere 
for  disposal. 

Of  course  there  may  be  cases  where 
sewage  disposal  seems  to  claim  preference 
to  water  supply,  in  the  use  of  a  stream. 
Each  of  these  must  be  adjusted  on  its  own 
merits.  The  willful  pollution  of  public 
water  supplies,  even,  if  it  seems  remote, 
should  no  longer  be  tolerated,  and  where 
new  sewerage  systems  are  being  built,  it 
is  unnecessary  that  it  should  be. 

Given  a  body  of  Avater,  not  used,  nor 
likely  to  be  employee!  for  a  public  water 
supply,  the  case  is  far  different.  Knowing 
the  amount  of  water  and  the  probable 
quantity  and  character  of  the  sewage,  it  is 


generally  ea»y  to  determine  whether  all 
the  crude  sewage  of  the  city  can  safely  be 
discharged  into  the  water  in  question. 
Averages  are  of  no  use  here.  The  water 
available  during  a  hot  dry  summer,  when 
the  stream,  pond  or  lake  is  at  its  lowest, 
and  banks  and  beds  are  exposed  to  the 
sun,  is  what  must  be  considered. 

Partial  purification  may  be  sufficient 
through  a  few  months  or  all  of  the  year 
for  some  cities,  and  works  have  been  car- 
ried out  on  that  basis.  But  most  plants 
in  this  country  have  been  built  under  con- 
ditions that  demand  continuous  operation 
at  their  utmost  efficiency. 

Where  sewage  is  discharged  into  large 
bodies  of  water,  either  lakes  or  the  ocean, 
it  is  generally  necessary  to  make  a  careful 
study  of  the  prevailing  currents  in  order 
to  determine  the  most  available  point  or 
points  of  discharge  in  order  to  prevent  the 
sewage  becoming  stagnant  in  bays  or  the 
washing  ashore  of  its  lighter  portions. 
Such  studies  are  commonly  made  by  floats, 
as  direction  of  current  is  generally  the 
factor  of  prime  importance. 


33 

When  it  is  decided  that  purification 
must  be  employed,  it  becomes  necessary 
to  select  the  method  best  suited  to  local 
needs  and  conditions.  This  matter  can 
better  be  discussed  after  the  subject  of 
purification  has  been  taken  up  in  detail, 
further  on,  and  so  will  be  dropped  for  the 
present. 

In  concluding  this  phase  of  the  subject, 
or  postponing  its  further  consideration,  it 
may  be  said  that  until  new  advances  have 
been  made  in  the  recovery  of  fertilizing 
matter  from  sewage,  no  compunction  need 
be  felt  in  discharging  such  into  any  body 
of  water  which  can  receive  it  without 
harm.  Where  such  water  is  available  it  is 
often  a  mere  question  of  the  relative  cost 
of  an  outfall  to  it  and  a  shorter  outfall 
with  purification  works  to  a  nearer  point 
of  discharge  where  purification  is  neces- 
sary. Of  course  treatment  of  the  sewage 
is  sometimes  the  only  course  which  has  a 
shadow  of  practicability.  Again  all  con- 
sideration of  such  a  procedure  is  often 
rendered  unnecessary  by  an  especially 
available  point  for  the  discharge  of  un- 


34 

purified  sewage.  Where  there  is  uncer- 
tainty it  is  best  to  keep  on  the  safe  side  and 
provide  purification  at  the  start.  Uncer- 
tainty to-day  in  these  matters  means 
certainty  in  favor  of  purification  to-mor- 
row, so  fast  are  we  advancing  in  sanitation 
and  so  rapid  is  the  increase  of  population 
and  also  of  the  pollution  of  our  streams. 

(5)  Population,  water  consumption,  and 
volume  of  sewage  for  which  provision 
should  be  made,  together  with  rainfall 
data  if  surface  drainage  is  to  be  installed- 

The  basis  for  population  studies  will  gen- 
erally be  the  United  States  census  for  a 
number  of  decades  past,  with  figures  for 
as  many  intermediate  years  as  possible 
filled  in  from  State  and  local  numerations. 
From  these  figures  percentages  of  growth 
for  decades  or  shorter  intervals  may  be 
computed  and  population  curves  plotted, 
and  from  one  or  both  of  these,  coupled 
with  present  local  conditions  and  future 
prospects,  the  population  for  the  next 
30  to  50  years  may  be  forecast  by  decades 
or  half  decades.  In  small  and  rapidly 


35 


growing  communities  it  must  be  remem- 
bered that  the  percentage  of  increase  is 
generally  less  as  the  population  becomes 
greater. 

It  is  desirable  to  design  a  sewerage 
system  large  enough  to  serve  for  a  number 
of  years  to  come,  say  30,  though  parts  of 
the  work  need  not  be  made  so  large,  as 
pumping  or  purification  works  where  either 
or  both  of  these  are  necessary. 

It  is  rarely  the  case  that  the  whole  popu- 
lation of  smaller  communities  is  connected 
with  the  sewers  until  years  have  elapsed 
after  the  construction  of  a  system.  This  is 
due  to  lack  of  sewers  on  some  streets  and 
to  that  strange  perversity  of  human  nature 
which  leads  many  people  to  put  off  the 
making  of  sewer  connections  as  long  as 
possible,  notwithstanding  the  fact  that  the 
soil  of  their  premises  is  daily  becoming 
more  and  more  polluted  with  excrementi- 
tious  matter,  and  that  the  yearly  expense 
of  properly  cleaning  privies  and  cesspools 
is  greater  than  the  interest  on  the  invest- 
ment necessary  for  making  sewer  connec- 


3G 


tions.  In  some  communities  allowances 
for  these  delays  may  be  made  in  designing 
pumping  or  purification  works,  but  the 
pipe  system  should  be  large  enough  at  the 
start  to  serve  each  street  and  district  for 
an  indefinitely  long  period.  The  advan- 
tages of  the  use  of  city  sewers  are  so  great 
that  all  property  is  bound  to  be  connected 
with  them  sooner  or  later,  leased  property 
without  these  conveniences  soon  dropping 
in  market  value.  In  view  of  these  facts 
the  population  figures  are  sometimes  based 
on  an  estimatad  number  of  people  per  acre, 
or  per  lineal  foot  of  sewer,  more  especially 
where  a  separate  system  of  sanitary  sewers 
is  being  constructed.  Safe  figures  of  the 
latter  class  cannot  be  laid  down  for  gen- 
eral application,  but  must  be  decided  on 
after  a  careful  study  of  the  community  in 
question,  the  character  of  its  residence 
property  and  general  population.  Often  it 
is  necessary  to  divide  a  city  into  districts 
for  its  population  and  rate  of  flow  studies. 
Thus  the  residence  sections  occupied  by  the 
wealthiest  classes  will  be  comprised  of  a 


37 

comparatively  small  population  per  acre, 
duo  to  the  large  size  of  the  lots.  The 
population  will  grow  more  dense  in  the 
passage  through  the  sections  occupied  by 
the  less  wealthy,  the  well-to-do  and  finally 
the  tenement  sections.  The  portions  of  a 
city  devoted  to  manufacturing  will  in  some 
cities  contribute  sewage  and  manufacturing 
wastes  in  pretty  close  proportion  to  the 
number  of  employers,  while  in  others,  or 
in  different  lines  of  industry,  the  sewage 
yield  will  vary  more  especially  with  the 
character  of  the  goods  being  produced. 

The  total  water  consumption  is  of  course 
mainly  dependent  upon  the  population, 
and  these  two  factors  together  enter  large- 
ly into  the  amount  of  sewage  requiring  re- 
moval and  disposal.  No  fixed  rule  can  be 
laid  down  for  water  consumption,  except 
that  in  general  it  is  on  the  increase  in  all 
American  cities,  and  in  many  places  has 
reached  immense  and  sometimes  alarming 
proportions.  It  may  be  kept  down  by  prop- 
er inspection  and  the  use  of  meters  for 
the  prevention  of  waste,  as  it  is  absolute 


38 

waste  and  not  beneficial  use  which  is  re- 
sponsible for  high  water  consumption. 

The  instances  are  rare  where  it  is  safe  to 
allow  for  less  than  60  gallons  per  capita 
per  day  as  the  average  water  consumption 
of  a  town,  if  most  of  the  people  patronize 
the  public  water  supply.  If  a  general  rule 
were  to  be  laid  down  100  gallons  would  be 
a  safer  figure.  Obviously  not  all  the  water 
which  passes  through  a  water- works  system 
reaches  the  sewers.  In  summer  much  of  it 
is  employed  for  lawn  and  street  sprinkling 
and  similar  purposes,  very  little  of  which 
reaches  the  sewers  even  where  the  com- 
bined system  is  in  use,  and  practically 
none  where  a  separate  system  of  sanitary 
sewers  is  employed.  But  while  all  this 
tends  to  diminish  the  sewage  yield  the  in- 
filtration of  ground  water,  already  dis- 
cussed, increases  it,  and  average  daily  fig- 
ures have  been  discussed  above,  while 
works  must  be  built  on  the  basis  of  maxi- 
mum daily,  or  even  hourly,  yields.  Alto- 
gether, then,  100  gallons  per  capita  will  be 
none  too  large  except  in  particular  cases  or 
possibly  for  the  immediate  present,  where 


39 


a  portion  of  the  works  can  be  built  for 
future  enlargement.* 

The  total  daily  flow  of  sewage  is  not 
distributed  evenly  through  the  24  hours. 
The  actual  percentages  at  different  hours 
of  the  day  vary  widely,  according  to  the 
nature  and  occupations  of  the  contributory 
populations.  In  most  towns  there  should 
be  scarcely  any  sewage,  if  the  sewers  are 
tight  enough  to  prevent  infiltration,  be- 
tween say  10  P.  M.  and  4  to  6  A.  M.,  a 
period  of  from  six  to  eight  hours.  As  a 
matter  of  fact  few  sewerage  systems  exist 
where  the  flow  during  these  hours  is  not 
considerable.  From  two-thirds  to  three- 
fourths  of  the  daily  flow  generally  occurs 
during  from — say  nine  to  twelve  hours  of 
the  day,  the  particular  hours  varying  some- 
what in  different  communities  and  having 
little  or  no  significance  in  designing  the 
smaller  portions  of  most  pipe  systems,  but 
affecting  the  outlets  and  being  of  great 


*  For  an  extended  study  of  vater  consumption,  with 
figures  for  a  large  number  of  American  municipalities 
and  with  much  other  data  on  tlie  relation  of  this  sub- 
ject and  of  population  to  amount  of  sewage,  see  Rafter 
&  Baker's  "Sewage  Disposal  in  the  United  States." 


40 

importance  where  the  sewage  must  be 
lifted  or  treated  before  its  final  discharge. 
Moreover,  there  are  generally  from  one  to 
three  hours  in  the  day  when  the  flow  is 
considerably  above  the  average  for  the 
heaviest  ten  hours.  The  actual  amount  of 
sewage  for  these  hours  must  be  taken  into 
consideration  in  the  separate  system  and 
the  plant  designed  accordingly.  For  ordi- 
nary laterals,  these  fluctuations  need  not 
be  taken  into  account,  for  in  the  best  prac- 
tice these  are  generally  more  than  ample 
for  their  duty.  As  the  sewers  increase  in 
size  and  territory  served,  and  as  disposal 
works  are  reached,  the  flow  during  max- 
imum hours  becomes  of  more  importance. 
Roughly  speaking,  10  per  cent,  of  the 
total  daily  flow  in  one  hour  may  be  con- 
sidered a  perfectly  safe  limit.* 

When  the  sewers  are  being  proportioned 
for  their  respective  streets  and  districts, 
density  of  population  must  be  considered. 
It  is  generally  necessary  to  arrive  at  this 

*  Staley  &  Pierson,  in  the  "  Separate  System  of  Sew- 
erage," givtt  ihu  maximum  hourly  flow  as  twice  the 
mean  hotirly  flow,  which  would  be  about  8  3  per  cent, 
of  the  total  daily  flow. 


41 


in  an  arbitrary  way,  as  actual  figures,  ex- 
cept for  the  whole  town,  are  seldom  avail- 
able except  in  communities  long  since 
sewered,  or  that  may  be  considered  as 
having  reached  their  full  growth.  The 
proper  figures  must  be  reached  for  each 
community  separately,  so  no  attempt  will 
be  made  to  give  them  here. 

Rainfall  data  are  liable  to  be  very  scarce 
in  all  but  the  larger  cities  and  towns,  and 
at  points  where  the  national  and  state 
weather  bureaus  have  stations  or  ob- 
servers. Such  defects  in  the  records  as  ex- 
ist through  lack  of  observations,  simply, 
cannot  be  remedied,  but  it  sometimes  hap- 
pens that  figures  for  near-by  towns  will  do 
very  well.  But  even  when  records  are 
available  they  may  not  be  sufficiently  de- 
tailed for  the  purposes  under  discussion. 
Monthly  or  weekly  totals  are  of  scarcely 
any  use,  and  even  daily  records  do  not 
completely  meet  the  necessities  of  the 
case.  What  is  desired  where  storm  sewers 
are  to  be  provided  is  the  duration  and  rate 
of  precipitation  of  the  heaviest  rains.  A 
very  heavy  shower  of  15  minutes  may 


42 

cause  more  inconvenience  and  damage,  if 
the  sewers  are  inadequate,  than  a  steady 
rain  extending  over  a  day  or  two.  There 
is,  of  course,  a  limit  to  the  size  of  sewers* 
imposed  by  financial,  and  in  some  cases  by 
physical  conditions.  Oftentimes,  where 
sharp,  heavy  rainfalls  occur,  their  complete 
speedy  removal  is  impossible,  and  the  sur- 
face water  simply  must  be  allowed  to 
stand  for  awhile.  Sewers  may  generally 
be  so  designed  that  they  will  speedily  re 
move  the  total  rainfall  except  at  long  in 
tervals  when  an  unusual  precipitation  oc^ 
curs. 

After  a  careful  study  of  all  the  rainfall 
records  available  and  a  consideration  of 
the  slope  and  character  of  tha  drainage 
area,  especially  whether  closely  built  up, 
with  paved  streets,  many  roofs,  small  areas 
in  forest  and  under  cultivation,  or  the 
contrary,  the  rate  of  rainfall  per  hour 
which  shall  furnish  the  basis  of  calcula- 
tions may  readily  be  decided  upon  by  any 
competent  engineer.  A  maximum  rate  of 
1  in.  per  hour  may  be  considered  as  a 
liberal  figure  in  some  localities.  The  pro- 


43 

portion  of  this  which  will  reach  the  sewers 
during  a  given  time  will  depend  upon  such 
local  factors  as  slope  of  land,  whether 
its  surface  is  covered  with  houses  and 
paved  streets,  cultivated  fields,  or  forests, 
and  the  permeability  of  such  soil  as  is 
exposed. 

(6)  Extent  and  cost  of  the  proposed 
system. 

This  is  a  matter  largely  dependent 
upon  the  local  treasury,  or  the  willing- 
ness of  the  people  to  incur  indebtedness, 
levy  general  taxes,  or  pay  special  assess- 
ments for  benefits,  as  the  case  may  be. 
The  ideal  plan  is  to  afford  every  build- 
ing in  the  community  an  opportunity  to 
connect  with  the  sewerage  system.  This 
cannot  often  be  done  at  the  start,  and  in 
most  instances  sparsely  settled  outlying 
districts  must  wait  long  and  weary  years 
before  the  sewers  reach  them,  although 
their  taxpayers  may  be  called  upon  year 
after  year  to  pay  taxes  to  redeem  i,he 
bonds,  meet  interest,  maintenance  and  re- 
pairs. The  oldest  and  most  thickly  settled 
portions  of  the  community  naturally  will 


44 

be  sewered  first,  after  which  the  system 
should  be  carried  as  far  out  in  various 
Directions  as  the  funds  available  will  per- 
mit. The  exact  course  followed  will  de- 
pend largely  upon  the  legislative  authority 
conferred  upon  a  given  municipality  to 
raise  money  for  sewerage  construction. 
Practice  in  the  several  States,  and  often  in 
the  various  cities  and  towns  of  one  State, 
varies  widely  in  these  particulars.  Some- 
times the  city  authorities  have  full  power 
to  lay  out  as  complete  a  system  as  they 
deem  best,  either  issuing  bonds  for  its  con- 
struction or  levying  assessments  for  bene- 
fits upon  abutting  property  owners  for  a 
part  or  the  whole  of  the  work.  Again, 
there  is  authority  only  for  the  construction 
of  trunk  sewers  and  other  works  for  final 
disposal,  the  building  of  laterals  depend- 
ing entirely  upon  the  initiative  of  property 
owners.  All  the  local  conditions,  legal 
and  otherwise,  must  be  ascertained  before 
the  extent  of  the  system  can  be  settled. 
All  work  should  be  planned  and  carried 
out  with  the  future  in  view  and  should  be 
complete  and  adequate  in  itself  and  in  re- 


45 

lation  to  other  parts  of  the  system,  so  that 
reconstruction  will  not  be  necessary  for 
years  to  come,  if  ever. 

It  appears  from  the  above,  and  from  a 
simple  common-sense  view  of  the  subject 
without  regard  to  what  has  been  written, 
that  the  extent  of  the  system  will  be 
governed  very  largely  by  the  local  pocket- 
book  and  existing  statutes,  and  that  it 
should  be  made  to  suit  the  most  pressing 
needs  of  the  community  and  be  capable  of 
easy  extension  as  soon  as  possible. 

The  cost  of  the  system  will  be  a  matter 
for  estimate  in  each  case.  Most  sewer  work, 
especially  for  sanitary  sewers,  is  so  simple, 
and  there  is  now  so  much  of  it  being  esti- 
mated upon  and  carried  out  by  engineers 
and  contractors,  that  it  is  comparatively 
easy  to  figure  up  the  approximate  cost  of 
a  sewerage  system.  Local  prices  of  labor 
and  freight  rates  on  sewer  pipe,  cement  and 
brick,  where  the  latter  is  used,  are  the 
main  factors,  and  must  be  decided  upon 
by  each  engineer  in  making  up  his  cost 
estimates.  The  technical  papers  now  pub- 
lish exhaustive  detailed  lists  of  bids  for 


46 

sewer  work  all  over  the  country,  and 
the  reports  of  city  engineers,  superintend- 
ents of  sewers,  sewerage  committees  and 
boards  of  public  works  often  abound  in 
figures  or  quantities  and  cost  of  work 
actually  done. 

(7)  Method  of  meeting  the  cost  of  the 
system. 

As  stated  above,  this  is  often  laid 
down  by  law,  so  that  there  is  little 
choice  to  be  had,  except  in  the  details. 
But  ample  latitude  is  sometimes  left  and 
generally  the  details  of  carrying  out  even 
fairly  definite  laws  afford  a  chance  for  a 
considerable  amount  of  variation,  together 
with  much  study. 

Broadly  speaking  there  are  two  methods 
of  raising  money  to  defray  the  cost  of  a 
sewerage  system :  (1)  By  making  the  work 
a  charge  upon  the  whole  municipality, 
raising  the  money  by  taxation  or  a  bond 
isssue;  and  (2)  assessing  the  cost  upon  the 
property  specially  benefited.  A  combina- 
tion of  these  plans  is  very  common.  The 
first  one  is  sometimes  put  into  effect  and 
the  second  with  comparative  infrequency, 


47 

except  for  single  streets  or  drainage  dis- 
tricts of  a  city  with  independent  outlets. 
The  trouble  with  the  second  plan  is  that  it 
is  not  easy  to  determine  the  proportionate 
amount  of  benefit  which  each  property 
owner  receives,  unless  it  be  in  the  most 
simple  cises. 

The  cost  of  constructing  and  operating 
a  water- works  system  is  met  by  the  yearly 
rentals  charged  for  water  furnished  the 
users  of  the  same,  but  the  general  aim  in 
the  case  of  sewers  is  to  make  their  use  as 
popular  as  possible.  Therefore,  the  most 
common  practice  in  this  country  has  been 
to  charge  nothing  for  using  the  sewer.  An 
entrance  fee,  sometimes  designed  to  repay 
the  city  the  cost  of  supervising  the  work, 
and  sometimes  intended  to  help  pay  for  or 
maintain  the  system,  is  often  charged  for 
connecting  with  the  sewers  and  paid  once 
for  all. 

The  actual  cost  of  house  connections  is 
always,  so  far  as  the  writer  knows,  borne 
by  the  house  owner. 

Where  the  general  public  and  the  prop- 
erty especially  benefited,  that  is,  actually 


48 


or  potentially  served  by  the  system  as  con- 
structed, share  the  cost,  it  is  divided  in 
various  proportions,  seemingly  without 
rhyme  or  reason,  in  many  instances.  It 
may  be  the  city  or  it  may  be  the  property 
benefited  that  pays  all  the  way  from  one 
to  three-fourths  of  the  cost,  or  perhaps 
through  a  wider  range.  With  the  separate 
system  of  sanitary  sewers  a  popular  plan 
and  an  apparently  fair  one,  where  the 
cost  is  simply  to  be  divided  as  stated 
just  above,  is  to  assess  upon  abutting 
property  the  cost  of  the  smallest-sized 
lateral  sewer,  or  in  other  words  of  a 
sewer  just  large  enough  to  serve  the 
houses  on  one  street  of  moderate  length. 
The  further  cost  of  the  system  or  ex- 
tensions, would  then  be  raised  in  the 
general  tax  levy  or  by  a  sale  of  bonds. 

The  assessments  for  benefits  are  levied 
upon  the  frontage  bordering  on  the  streets 
in  which  the  sewers  are  laid,  or  upon  the 
area  of  th'e  lots,  or  are  divided  between 
these  methods.  The  whole  subject  under 
discussion  is  a  complicated  one  and  has 


49 


never  received  the  consideration  it  deserves 
from  municipal  officers.* 

But  to  one  such  an  official,  great  credit 
should  be  given  for  having  made  a  very 
exhaustive  investigation  of  the  problem 
and  presented  a  solution  which  aims  to  be 
fair,  conducive  to  the  rapid  extension  and 
use  of  his  particular  sewerage  system,  and 
in  many  points  admirably  adapted  to  other 
localities.  This  study  was  made  by  Mr. 
F.  H.  Snow,  City  Engineer  of  Brockton, 
Mass.,  and  the  plan  recommended  was 
adopted  by  that  city.  A  summary  of  Mr. 
Snow's  report  is  given  below,  the  import- 
ance of  the  subject,  the  lack  of  both  popu- 
lar and  technical  information  regarding  it, 
and  the  value  of  the  report  itself,  seeming 
to  warrant  the  devotion  of  a  few  pages  to 
this  purpose. f 

The  population  of  Brockton  is  about 
30,000.  The  sewerage  system  includes  a 


*  A  monograph,  entitled  "Special  Assessments,"  by 
Victor  Kosewater.  (Columbia  College  Studies  in  History, 
Economics  and  Public  Law)  will  be  of  interest  and  value 
to  those  who  wish  to  pursue  the  general  subject  further. 

t  This  summary  is  condensed  from  an  editorial  digest 
and  discussion  by  the  writer  which  appeared  in  "  Engin- 
eering iVeutt"  of  Ju  y  19,  1894. 


50 


receiving  reservoir,  pumping  station,  force 
main  and  filter  beds.  The  first  cost  of  the 
system,  so  far  as  constructed,  was  raised 
by  an  issue  of  bonds.  The  summary  is  as 
follows  : 

In  arriving  at  the  proper  plan  for  Brockton,  Mr. 
Snow  studied  with  great  care  the  various  methods 
of  assessments  already  in  use,  after  first  having 
shown  that  the  benefits  of  a  sewerage  system  were 
partly  public  and  partly  private,  and  should  be 
borne  accordingly.  Public  benefits  are,  of  course, 
to  be  met  by  general  taxation.  The  proportion  to 
be  paid  by  the  public  has  been  fixed  by  the  Massa- 
chusetts legislature  at  not  less  than  one-fourth  nor 
more  than  two-thirds  of  the  total  cost  of  the  sewer- 
age system.  For  private  benefits  a  variety  of 
methods  are  permitted  by  the  statutes,  such  as 
frontage  and  area  assessments,  yearly  rentals, 
entrance  fees,  or  a  combination  of  these. 

****** 

Either  the  frontage  or  the  area  plan  alone  is 
shown  by  Mr.  Snow  to  be  inequitable,  diagrams 
being  used  to  illustrate  how  by  either  plan  differ- 
ences in  the  shape  of  lots  may  allow  several  houses 
on  one  lot  and  only  one  or  two  on  another,  each 
lot  having  the  same  area  or  frontage,  as  the  case 
may  be.  The  entrance  fee  is  also  shown  to  be 
unjust,  unless  it  is  graded  in  accordance  with  bene- 
fits received,  while,  •  in  addition,  a  large  fee  would 


51 


be  required  at  the  start,  when  there  were  but  few 
connections,  or  else  reliance  on  the  general  tax 
levy  would  be  necessary . 

The  method  finally  recommended  by  Mr.  Snow 
is  given  in  his  report  as  follows  : 

It  is  recommended  that  one-fourth  of  the  total 
cost  of  the  sewerage  system  be  raised  by  first 
assessment,  one-half  by  rental,  and  the  remainder 
by  general  tax.  It  is  also  recommended  that  first 
assessmant  be  based  on  area  and  frontage  of  land 
adjacent  to  sewers  — 0.6  on  area  within  125  ft.  of 
the  street  line  and  0  4  on  frontage  ;  that  the  first 
assessment  be  collected  in  one  payment  and 
credited  to  construction  account ;  that  the  unit  of 
rental  be  1,000  gallons  of  water  reaching  the 
sewer,  this  to  be  ascertained  from  meter  gagings 
of  the  water  department,  and  to  be  corrected  for 
water  finding  another  outlet  than  the  sewer  by  a 
system  of  discounts ;  70  per  cent,  to  be  deducted 
from  water  supply  of  shops  and  20  per  cent,  from 
water  supply  of  houses  having  sill-cocks. 

And  it  is  further  recommended  that  abuttors  be 
not  compelled  to  enter  the  sewer  as  soon  as  com- 
pleted ;  that  no  one  be  allowed  to  enter  without  a 
permit  ;  that  no  rent  be  charged  users  before  Jan- 
uary 1,  189.5,  rents  starting  from  that  date  ;  that 
such  rents  be  charged  from  the  first  of  the  month 
following  that  in  which  the  permit  is  dated  ;  and 
that  all  deficiencies  be  made  up  in  the  early  years 
by  general  tax  levy. 

It  is  further  recommended  that  the  following 
prices  be  assessed  per  unit  :  For  first  assessment, 
0.3  cents  per  square  foot,  and  15  cents  per  front 
foot;  for  rental,  28  cents  per  1,000  gallons  enter- 
ing the  sewer  ;  and  that  $8.40  be  charged  for  un- 
metered  connections,  subject  to  a  discount  of  20 
per  cent,  for  sill-cocks. 


These  first  assessments  represent  the  value  of 
the  sewerage  system  to  land,  in  enhancing  its  price 
without  regard  to  whether  the  sewers  are  used  by 
the  owners  of  the  land.  The  amount  raised  by 
general  taxation  will  likewise  represent  the  benefit 
to  the  community  as  a  whole,  without  regard  to 
the  locat'on  of  the  sewers.  Benefits  from  actual 
use  of  the  sewers  are  to  be  paid  by  rental,  acsord- 
ing  to  the  amount  of  sewage  contributed,  and  the 
sums  so  raised  will  be  applied  to  paying  off  the 
bonds,  meeting  interest  and  to  maintenance.  The 
rentals  will  pay  two-thirds  of  the  total  yearly 
charges,  leaving  the  balance  to  be  met  by  general 
taxation. 

It  is  eminently  fitting  that  rental  should  be 
based  on  the  amount  of  sewage  contributed,  since 
upon  the  latter  depends  the  size  of  the  sewers,  and 
notably  the  cost  of  constructing  and  operating  the 
pumping  plant  and  filter  beds.  Fortunately  at 
Brockton  G5  per  cent,  rf  the  water  connections 
are  metered  and  the  records  of  the  water  depart- 
ment are  well  kept,  so  that  the  sewer  rentals  can 
easily  be  based  on  the  water  consumption.  Obvi- 
ously on  many  premises  some  of  the  water  used 
does  not  find  its  way  to  the  sewers,  hence  the  pro- 
posed deduction  of  20  per  cent,  of  the  consump- 
tion for  houses  having  sill-cocks  for  hose  and  of 
70  per  cent  for  shops. 


53 


The  unit  of  28  cts.  per  1,000  gallons  of  water 
was  arrived  at  by  computing  the  probable  yearly 
expenses  of  the  sewerage  system  until  1900  and  the 
probable  water  comsumption  for  the  same  period. 
It  should  be  stated  that  the  water  consumption  in 
Brockton  is  phenomenally  low,  only  25  gallons  p(  r 
capita.  The  yearly  rate  of  $8.40  for  unmetered 
houses  was  chosen  because  the  minimum  rates  for 
metered  water  are  such  as  to  make  it  an  object  to 
water  users  to  have  a  meter  when  the  water  con- 
sumption goes  above  a  point  that  would  call  for 
such  a  rental. 

Coming  to  the  amount  to  be  raised  yearly  in  the 
tax  levy,  the  problem  is  simple,  the  amount  being 
the  difference  between  the  total  amount  to  be 
raised  and  that  provided  for  as  outlined  above. 

Although  this  system  has  been  worked  out  to 
meet  the  situation  of  Brockton,  which  is  in  a  num- 
ber of  respects  unique,  the  general  principles 
involved  may  be  applicable  in  other  places.  The 
special  conditions  at  Brockton  are  as  follows;  (1) 
No  sewers  are  yet  in  use,  although  the  city  has  a 
population  of  about  30,000;  this  renders  possible 
the  adoption  of  any  desirable  system  without  the 
unfairness,  real  or  fancied,  which  follows  a  change 
in  the  case  of  old  systems.  (2)  It  is  expected  that 
the  whole  city  will  be  sewered  in  a  comparatively 
few  years,  so  that  the  total  cost  of  the  system  can 
be  readily  estimated,  which  is  essential  to  this 
plan.  (3)  The  large  percentage  of  metered  water 


54 


taps  and  the  fact  that  the  city  owns  the  water- 
works, so  that  water  and  sewer  departments  can 
co-operate,  while  each  desires  to  keep  the  water 
consumption  down,  are  favorable  to  a  yearly 
rental  plan,  based  on  water  consumption.  Modi- 
fications of  these  conditions  might  make  the 
system  difficult  of  application  or  might  cause  fric- 
tion when  applied.  Nevertheless-  the  principles  at 
the  bottom  of  it  seem  correct,  and  this  general 
distribution  of  the  burden  of  a  sewerage  system, 
whether  in  these  or  other  proportions,  seems  fair 
and  likely  to  be  popular.  General  public  and 
individual  private  benefit  are  each  recognized  and 
the  latter  is  divided  into  two  classes,  (1)  potential 
benefit  through  increased  value  of  a  certain  piece 
of  property  because  the  sewer  passes  by  it  and  may 
be  used,  and  (2)  the  actual  benefit  through  use. 

Two  dangers  which  beset  the  extremes  of  the 
two  methods  most  usually  employed  to  raise 
money  for  sewers  seem  likely  to  be  counteracted 
to  a  large  extent  by  this  plan:  (l)  When  the 
•whole  cost  is  put  in  the  general  tax  levy  or  is  met  by 
bonds,  the  interest  and  principal  of  which  must  be 
met  by  taxes,  it  is  difficult  to  secure  money  for  exten- 
tensions,  every  taxpayer  wishing  to  keep  the  rate 
down,  and  those  living  on  sewered  streets  having 
no  direct  interest  in  extensions.  In  the  Brockton 
plan  the  t~x  levy  is  increased  by  only  one-fourth 
the  total  cost  of  the  sewers,  the  bulk  of  the  ex- 
penditure being  put  upon  those  whose  land  is 


55 


improved  or  those  who,  by  use  of  the  sewers,  are 
saved  the  expense  of  cleaning  cesspools  or  privy 
vaults.  The  taxpayer  feels  that  the  sewerage 
system  is,  to  large  extent,  self-sustaining,  like  a 
municipal  water-works  plant.  (2)  The  other 
danger  is  that  where  property  benefited  bears  the 
whole  expense  of  sewers  it  will,  in  case  of  assess- 
ments for  frontage  or  area,  try  to  keep  the  sewer 
out  of  the  street.  But  in  Brockton  a  given  prop- 
erty owner  will  be  paying  towards  one-fourth  the 
cost  of  the  system  whether  the  sewers  are  in  his 
street  or  not,  and  once  in  his  street  he  need  pay 
only  an  additional  one-fourth  for  property  benefit, 
unless  he  wishes  to  connect  with  the  sewer.  The 
sewer  once  in,  however,  he  will  already  be  paying 
towards  one-half  of  the  total  cost  of  the  system  and 
the  additional  expense  for  the  use  of  the  sewer  will 
seem  small.  Moreover,  by  economy  in  the  use  of 
water  his  rental  may  be  kept  low,  and  most 
people  do  not  consider  themselves  extravagant 
water  users. 

(8)  The  needs  of  sewerage  peculiar  to 
the  locality^  with  a  study  of  the  health  and 
mortality,  of  the  town. 

Little  need  be  said  on  these  phases  of 
the  subject.  The  adoption  of  a  scheme 
and  the  raising  of  money  for  its  realization 
may  be  greatly  aided  by  showing  that 
local  conditions  imperatively  demand  the 


-56 

improvement.  A  study  of  the  health  and 
mortality  of  the  town,  and  comparisons  of 
the  results  with  like  studies  of  communi- 
ties enjoying  good  sewerage  systems  is 
often  helpful  in  enlisting  popular  enthu- 
siasm for  sanitary  progress.  But  such 
work  must  be  done  wisely  and  false  state- 
ments and  impressions  regarding  the  rela- 
tion between  unsanitary  conditions  and 
disease  avoided  as  one  would  shun  poison. 
There  has  been  so  much  ranting  of  late  re- 
garding deadly  disease  germs  lurking  here, 
there  and  everywhere  that  many  persons 
on  reflecting  that  they  and  most  of  their 
neighbors  still  live,  grow  suspicious  and 
feel  inclined  to  discredit  the  germ  theory 
of  disease  and  the  advantage  of  cleanliness 
in  all  the  departments  of  life.  It  must  be 
remembered  that  just  as  there  are  thou- 
sands of  visible  forms  of  plant  life,  of 
which  only  a  very  small  percentage  are 
poisonous,  so  among  the  many  invisible 
forms  of  plant  life  known  as  bacteria  or 
microbes  there  are  only  a  few  harmful 
germs.  These ,  few,  it  must  be  taught, 
give  rise  to  dire  results  when  allowed 


57 


access  to  private  water  supplies,  like  house- 
wells,  through  leaching  privies  and  cess- 
pools, or  to  public  water  supplies  by  dis- 
charging crude  sewage  into  streams  or 
lakes  from  which  such  supplies  are  drawn. 
Furthermore,  unsanitary  conditions,  while 
not  giving  rise  to  certain  forms  of  disease, 
may  render  the  human  system  unfit  to  ward 
off  attacks  of  the  same.  Facts  like  these, 
reasonably  presented,  may  sometimes  do  a 
world  of  good  in  an  engineer's  report, 
while  the  too  common  exaggerations  would 
disarm  instead  of  assure  the  people. 

ADOPTION  OF  THE  ENGINEER'S  REPORT. 

The  report  of  the  engineer  having  been 
completed  and  submitted  to  the  proper 
officials  its  adoption  by  them  them  may  be 
assumed.  Sometimes  the  plan  recom- 
mended has  to  be  submitted  to  a  popular 
vote,  but  more  often  where  a  vote  is  taken 
it  is  only  indirectly  upon  the  specific  plans 
proposed,  the  real  question  being  whether 
bonds  shall  or  shall  not  be  issued  for  the 
execution  of  the  scheme.  After  the  gene- 
ral report  is  adopted  the  next  step  is  to 


58 

select  an  engineer  to  prepare  detailed 
plans  and  specifications  preparatory  to 
advertising  for  bids  from  contractors. 
Frequently  the  engineer  who  made  the 
preliminary  studies  is  engaged  as  design- 
ing engineer  and  sometimes  to  supervise 
construction  as  well.  This  course  has 
the  advantage  of  continuing  the  services 
of  one  more  or  less  familiar  with  local 
conditions,  and  with  the  plan  for  sewer- 
ing the  town  already  partially  worked 
out. 

DESIGN  AND  CONSTRUCTION  OF  THE  CON- 
DUIT SYSTEM. 

The  first  work  of  the  engineer  will  be 
to  design  his  pipe  or  conduit  system.  For 
this  task  the  topographical  map  already 
mentioned  will  be  a  help,  but  this  should 
be  supplemented  by  a  profiles  of  all  the 
streets  in  which  sewers  are  to  be  laid,  in 
order  that  the  proper  grades  may  be  deter- 
mined and  the  accessories  of  the  systems 
designed. 

Numerous  diagrams  and  tables  are  avail- 
able for  use  in  designing  conduit  systems, 


59 

rendering  separate  computations  with  the 
aid  of  complicated  formulae  altogether  un- 
necessary, unless  the  engineer  wishes  to 
make  his  own  figures.*  In  the  separate  sys- 
tem it  is  generally  best  to  use  8-in.  pipe  as 
the  minimum  size,  in  order  to  lessen  the 
risk  of  stoppages,  although  6  ins.  is  ample 
for  the  volume  of  sanitary  sewage  from  an 
ordinary  residence  street  of  medium  length. 
Pipe  sewers  are  generally  made  of  vit- 
rified clay,  with  a  salt-glazed  surface. 
Cement  pipe  (cement  and  sand)  is  also 
used 'in  some  cities.  The  size*  of  pipe 
sewer  was  for  many  years  limited  to  a 
diameter  of  24  ins.  but  some  of  the  manu- 
facturers now  make  pipe  36  ins.  in  diam- 
eter for  general  use.  The  24  in.  limit  was 
in  force  because  of  the  difficulty  and  ex- 
pense of  making  the  larger  pipe  and  the 
comparative  ease  of  laying  brick  sewers  of 
any  size  from  24  ins.  up.  Monolithic  sewers 

*  Mathematical  dipcussions  of  sewer  formulae  are  beyond 
the  bcope  of  this  work.  See  Baumeister's  "Cleaning  and 
Sewerage  of  Cities  "  for  a  brief  but  able  presentation  of  the 
subject,  illustrated  by  diagrams,  and  Flynn's  "Flow  of 
Water  in  Open  Channels,  Pipers  Sewers,  Conduits,  etc.,"  for 
tables.  Staley  &  Piersou's  ' '  Separate  Systems  of  Sewerage  " 
may  also  be  consulted.  More  recent  books  are  "  Ogden's 
Sewer  Design  "  and  FolwelTs  Sewerage." 


60 

have  been  used  for  a  limited  extent,  the 
conduits  being  built  in  place  from  cement 
mortar.*  In  very  wet  ground  cast  iron 
pipe  with  lead  joints  is  used,  either  be- 
cause it  is  specially  desirable  to  prevent 
infiltration  or  because  of  fear  of  damage 
through  settlements. 

The  pipe  should  be  laid  to  grade  with 
great  care,  and  a  good  alignment  should 
be  secured.  Holes  should  be  dug  for  the 
bells  of  the  pipe  so  that  each  length  of 
the  latter  will  have  a  solid  bearing  through- 
out. When  the  material  is  such  as  to  make 
uncertain  a  solid  support  for  the  pipe,  sand, 
gravel,  concrete,  plank  or  piles  should  be 
employed  for  the  purpose.  If  rock  is  en- 
countered in  trenching,  it  will  Le  necessary 
to  provide  a  bed  for  the  pipe  which  will 
not  be  washed  into  fissures  by  the  stream 
of  sub-soil  water  which  is  likely  to  follow 
the  eewer  when  the  ground  is  saturated.  At 
Little  Falls,  N.  Y.,  in  the  case  of  a  vitri- 
fied pipe  line  for  a  water  supply  conduit, 
such  a  washing-out  of  material  occurred, 

*  Concrete,  both  plain  and  reinlomd  vith  steel,  has  bt-en 
coming  into  n*e  since  the  lit  »t  ed.tion  c  f  this  book  was  \N  rit- 
uu  (it>U5;,  but  u.ore  puniculaily  for  large  fcew<,is. 


61 


causing  settlements  and  the  pulling  apart 
of  joints.  The  trench  was  opened  through 
the  rock  portion  and  the  pipe  embedded  in 
concrete. 

SUBSOIL  DRAINS,  OR  UNDERDRAINS. 

Where  sewers  are  in  wet  sand  or  gravel, 
subsoil  drains,  or,  as  they  are  more  usually 
called,  underdrains  may  be  laid  beneath  or 
alongside  the  sewer  to  advantage,  as  dis- 
cussed above.  These  are  generally  simple 
agricultural  tiles  from  3  ins.  in  diameter 
upward.  They  have  no  joints,  being 
simply  hollow  cylinders,  and  are  laid  with 
their  ends  a  fraction  of  an  inch  apart, 
wrapped  with  a  cheap  so-called  muslin 
cloth,  or  other  suitable  material  to  keep 
out  the  dirt  until  the  matter  in  the  trench 
becomes  thoroughly  packed  about  them. 
These  underdrains  may  almost  always  be 
emptied  into  the  nearest  stream,  provided 
it  is  not  used  as  a  public  water  supply. 
This  qualification  is  on  account  of  the  fact 
that  the  sewers  may  leak  and  sewage  thus 
flow  directly  into  the  underdrains.  Such 
danger  may  seem  remote,  but  it  was  con- 


62 

sidered  sufficient  to  cause  the  city  of  Bos- 
ton to  refuse  to  pay  a  promised  sum  toward 
the  cost  of  the"  sewers  of  South  Framing- 
ham,  Mass.,  so  long  as  the  sewer  under- 
drainge  discharged  into  a  stream  tributary 
to  one  of  the  sources  of  the  Boston  water 
supply.  Boston  had  agreed  to  make  this 
contribution  in  order  to  induce  the  town 
of  Framingham  to  remove  -its  sewage 
from  the  Boston  water  works.  This  made 
purification  necessary,  which  in  turn  de- 
manded that  all  the  sewage  should  be 
pumped  to  the-  filter  beds  and  irrigation 
area.  Naturally  the  town  did  not  wish 
to  pump  and  purify  the  underdrainage,  but 
after  some  years  of  delay  and  an  offer  of 
an  additional  sum  from  the  city  of  Boston 
the  town  constructed  reservoirs  and  filter 
beds  for  the  purification  of  the  underdrain- 
age, all  of  which  must  be  pumped  a  small 
lift. 

Perhaps  one  of  the  best  examples  of 
subsoil  drains  beneath  sanitary  sewers,  or 
at  least  the  best  example  which  has  been 
described  and  illustrated  in  detail,  is  at 


63 

Newton,  Mass.,  where  drains  were  placed 
below  many  miles  of  sewers.* 

MANHOLES. 

Manholes  should  be  placed  at  all  changes 
of  grade  and  at  all  junctions  between  two 
or  more  street  sewers.  These  are  built  of 
brick  and  afford  access  to  the  sewer  for 
inspection.  In  addition  they  are  some- 
times used  for  flushing.  They  are  pro- 
vided with  iron  covers,  the  latter  often 
being  pierced  with  holes  to  afford  ventila- 
tion to  the  sewers.  When  the  covers  are 
so  perforated  pails  are  often  suspended 
beneath  to  catch  the  dirt  from  the  street 
surface,  especially  when  the  manholes  are 
in  macadamized  gravel  or  dirt  streets. 

On  long  stretches  of  straight  sewers 
lampholes  are  somtimes  put  in  between 
manholes,  consisting  generally  of  a  vertical 
piece  of  pipe  extending  from  the  sewer 
nearly  to  the  surface  and  provided  with  a 
cover.  These  are  valuable  aids  to  in- 
spection. 

*  See  Engineering  News,  January  2,  1896,  for  illustrated 
description  of  this  system. 


64 

SEWER  GRADES. 

The  grades  of  sewers  should  be  sufficent, 
where  possible,  to  give  them  a  self-cleans- 
ing velocity,  thus  rendering  stoppages  from 
ordinary  suspended  matters  impossible. 
Baumeister,  in  his  "  Cleaning  and  Sewer- 
age of  Cities,"  makes  the  following  state- 
ments on  this  subject: 

Practical  experiments  show  that  sewers  of  the 
usual  sections  will  remain  clean  with  the  follow- 
ing minimum  grades:  separate  house  connec- 
tions, 2  per  cent.  ;  extreme  cases,  1  per  cent. 
Small  street  sewers,  1  per  cent.  ;  extreme  cases, 
0.7  percent.  Main  sewers,  0.7  per  cent.  ;  ex- 
treme cases,  0.5  per  cent.  The  extreme  cases  are 
for  sewers  carrying  only  rain  or  quite  pure  water. 

The  following  empirical  formula  will  give  the 
minimum  grade  for  a  sewer  of  clear  diameter 
equal  to  d  inches  and  either  circular  or  oval  in 
section : 

100 
Minimum  grade,  in  per  cent  ~r>_i_ro 

FLUSHING  DEVICES. 

Where  very  low  grades  are  unavoidable 
and  at  the  heads  of  branch  sewers  where 
the  volume  of  flow  is  small,  flushing  may 
be  used  with  advantage.  In  some  cases  a 


65 

copious  supply  of  water  is  turned  into  the 
sewer  through  a  manhole  from  some 
stream,  pond  or  lake,  or  from  the  public 
water  works  system.  Generally,  however, 
the  water  introduced  is  allowed  to  accu- 
mulate before  discharge,  being  held  back, 
for  instance,  by  plugging  up  the  lower 
side  of  a  manhole  until  the  water  accumu- 
lates in  it,  then  suddenly  withdrawing  the 
plug  and  releasing  the  water,  upon  which  it 
rushes  down  the  sewer  carrying  before  it 
practically  all  obstructions,  except  in  ex- 
treme cases. 

Instead  of  relying  upon  clear  water,  as 
described  above,  it  may  l,e  sufficient  at 
some  points  on  the  system  to  simply  back 
up  the  sewage  by  plugging  the  manhole 
outlet,  thus  flushing  the  sewer  with  the 
sewage  itself. 

The  necessity  of  frequent  and  regular 
flushing  has  given  rise  to  automatic  flush- 
ing tanks.  These  generally  make  use  of 
the  siphon  for  self-discharge,  although 
there  is  on  the  market  a  purely  gravity 
flush  tank,  which  tips  by  its  own  weight 
when  full.  Whatever  the  means  of  dis- 


charge  the  feed  to  the  tank  is  regulated  by 
a  valve  or  cock  on  the  supply  pipe,  so  the 
tank  will  fill  and  empty  once  in  a  given 
number  of  hours. 

Y-BKANCHES     FOR   HOUSE     CONNECTIONS. 

Provision  for  house  connections  should 
be  made  when  laying  sewers,  in  order  to 
avoid  as  much  as  may  be  tearing  up  the 
streets  after  the  pipe  system  is  in  and  the 
breaking  of  holes  into  the  sewer.  It  is  a 
wise  plan  to  lay  the  house  connections 
from  the  street  sewer  to  the  curb,  or  even 
across  the  sidewalk,  while  the  street  is  dug 
up.  At  the  least  Y-branches  for  house 
connections  should  be  put  in  at  frequent 
intervals,  say  from  25  ft.  apart  upwards, 
according  to  the  character  of  the  street. 
When  the  sewer  is  put  down  deep  quarter 
bends  are  sometimes  provided  and  the 
house  connection  pipe  carried  vertically 
upwards  until  within  a  few  feet  of  the  sur- 
face to  avoid  deep  digging.  However  the 
house  connection  may  join  the  sewer,  or 
any  two  sewers  join  each  other,  the  direc- 
tion of  flow  in  connection  and  street  sewer 


67 

should  be  as  nearly  the  same  as  possible, 
and  the  entering  sewer  should  be  at  a  little 
higher  level  than  the  sewer  entered  in 
order  to  increase  the  velocity  of  the  in- 
fluent sewage  and  thus  lessen  the  tendency 
to  retardation  and  stoppage  which  natu- 
rally results  where  two  confined  streams 
with  matters  in  suspension  unite. 

DEPTH   OF   SEWERS   BELOW    SURFACE   OF 
GROUND. 

No  general  rule  can  be  laid  down  for  the 
depth  of  sewers  further  than  that  they 
must  be  deep  enough  to  :idmit  of  house 
connections  with  a  proper  fall,  and  on  the 
other  hand  should  be  p.s  near  the  surface 
as  possible  to  save  the  expense  of  deep 
trenching.  Of  course  they  must  be  kept 
below  the  point  at  which  clanger  from 
freezing  might  arise,  but  the  natural 
depth  is  usually  sufficient  to  make  such  a 
consideration  unnecessary,  especially  as  the 
temperature  of  sewage  is  generally  a  num- 
ber of  degrees  above  that  of  the  atmos- 
phere at  the  street  surface. 


68 


VENTILATION  OF  SEWEKS. 

The  ventilation  of  sewers  is  a  subject 
still  fraught  with  many  fears  and  per- 
plexities. In  the  early  days  of  sewers  the 
conduits  were  faulty  in  the  design  of  their 
cross-sections,  in  their  grades  and  in  their 
construction.  Practically  all  of  these  con- 
duits originally  carried  surface  water,  and 
through  infiltration  large  quantities  of 
ground  water.  Many  of  these  conduits, 
as  stated  at  the  beginning,  were  built  to 
carry  storm  water  alone,  in  other  words 
were  simply  drains.  With  the  advent  of 
ample  public  water  supplies  and  modern 
plumbing,  which,  with  its  many  fixtures 
providing  hot  and  cold  water  at  every 
hand  led  to  high  water  consumption, 
houses  were  connected  with  the  drains, 
thus  converting  them  into  sewers.  Still 
later,  the  convenience  of  this  practice  being 
recognized,  conduits  were  designed  and 
built  to  carry  both  drainage  and  sewage, 
but  these  sewers  on  what  we  now  call  the 
combined  system  were  little  or  no  better 
in  design  and  construction  than  the  old 


69 

surface  drains.  The  consequence  of  all 
this  was  that  the  uneven  bottoms  made 
long  stretches  of  sewer  little  or  no  better 
than  cesspools,  and  this  cause,  with  poor 
construction,  gave  rise  to  stoppages  which 
still  further  aggravated  the  stagnation. 
Decomposition,  without  the  presence  of  a 
plentiful  supply  of  oxygen,  evolved  offen- 
sive gases,  which  sought  the  upper  air 
through  all  possible  channels.  Street  in- 
lets for  surface  water  and  manholes  for 
cleaning  belched  forth  gases  whose  malo- 
dorous presence  was  easily  recognized.  Too 
often  these  odors  were  noticeable  in  houses. 
To  prevent  such  a  state  of  affairs  various 
methods  of  sewer- ventilation  were  tried, 
which  it  is  unnecessary  to  describe  here. 
In  modern  work  of  good  design  sewers  are 
built  with  the  intention  of  removing  all 
sewage  immediately  before  offensive  de- 
composition has  time  to  begin.  The 
grades  are  as  nearly  perfect  as  possible, 
the  interiors  are  reasonably  smooth  to 
prevent  adhesion  of  putrescible  matter, 
and  the  manholes  have  perforated  covers 
to  aid  in  ventilation.  In  some  cities  ven- 


70 


tilating  shafts  are  provided  to  supplement 
the  manholes,  these  sometimes  being  the 
soil  pipes  of  the  houses,  the  main  trap 
being  omitted  for  this  purpose.  The  latter 
practice  is  recommended  by  some  of  the 
best  engineers  and  sanitarians  of  the  day, 
the  theory  being  that  by  such  means  well 
constructed  sewers  are  kept  so  filled  with 
fresh  air,  and  so  free  from  bad  gases,  that 
no  harm  can  arise  if  occasionally  a  trap  to 
some  wash  bowl  or  water  closet  fails  and 
the  sewer  air  reaches  a  dwelling  room. 
But  notwithstanding  these  opinions  the 
majority  of  sanitarians  still  object  to  ven- 
tilating sewers  through  houses  and  insist 
upon  the  main  trap. 

It  seems  obvious  that  in  the  separate 
system  of  sewers,  with  its  small  laterals,  a 
4-in.  ventilating  pipe  is  not  needed  every 
50  or  100  ft.  on  both  sides  of  the  street  to 
change  the  air  in  a  10,  8,  or  even,  as  is 
sometimes  the  case,  a  G-in.  street  sewer. 
The  most  common  practice  is  to  assess  the 
whole  or  a  considerable  portion  of  the 
cost  of;  such  small  sewers  upon  abutting 
property  owners.  Where  this  is  done  it 


71 

may  be  difficult  to  say  to  one  man  out  of 
perhaps  five,  "you  must  for  the  general 
good  omit  the  usual  main  trap  from  your 
soil  pipe  in  order  that  the  street  sewer 
may  be  ventilated ;  or  if  you  object  to 
that  you  may  run  a  separate  ventilating 
pipe  from  your  house  sewer  at  a  point  just 
outside  your  main  trap  to  the  top  of  ,ypur 
roof."  Naturally,  most  men  would  object 
to  such  an  alternative,  preferring  not  to 
risk,  as  they  might  think,  with  ample 
support  from  engineers  and  others  sup- 
posed to  know,  the  lives  of  themselves 
ana  their  families,  nor  to  spend  money  to 
avoid  such  a  risk  while  four  of  their 
neighbors  were  not  called  upon  for  either 
risk  or  sacrifice.  To  be  sure  some  means 
might  be  devised  to  assess  the  cost  of 
these  extra  pipes  upon  the  town  at  large, 
where  the  people  refused  to  allow  the 
ventilation  through  their  soil  pipes,  but 
this  would  give  rise  to  some  trouble,  at 
the  best,  so  that  the  wisest  course  might 
be  to  provide  extra  ventilation,  if  ex- 
perience showed  it  necessary,  entirely  at 
town  expense,  and  independently  «f  dwell- 


ings.    The  matter  of  ventilation  is  further 
discussed  at  the  end  of  the  next  section. 

MISAPPREHENSIONS  REGARDING  SO-CALLED 
SEWER  GAS. 

Before  leaving  this  subject  a  few  words 
seem  necessary  regarding  misapprehen- 
sions on  the  question  of  so-called  sewer  gas 
and  the  conveying  of  disease  germs  there- 
by. And  first,  there  is  no  specific  and  defin- 
ite sewer  gas  for  which  a  chemical  formula 
or  combination  of  symbols  can  be  laid 
down.  The  air  in  sewers  contains  in  greater 
or  less  degree  some  of  the  gaseous  products 
of  decomposition  whenever  chemical 
changes  are  taking  place  in  the  organic 
matter  conveyed  by  or  deposited  in  the 
sewers.  This  air  is  harmful  if  breathed, 
just  the  same  as  any  other  foul  air,  and  to 
no  greater  extent,  except  for  the  slight 
possibility  that  it  may  contain  harmful  bac- 
teria. The  disease  germs  which  may  be 
expected  in  sewage  are  essentially  water- 
borne  instead  of  air-borne,  and  develop  in 
the  human  intestines  rather  than  in  the 


73 

throat,  nose  or  lungs,  and  therefore  gain 
access  to  man  chiefly  tli rough  food  and 
drink.  The  germs  carried  by  so-called 
sewer  gas  must  obviously  be  air-borne  and 
from  their  origin  are  not  likely  to  be  found 
in  sewage,  or  if  found  they  would  be  in 
small  quantities ;  but  while  all  this  is  true 
it  does  not  make  sewer  air  any  more  de- 
sirable for  breathing.  The  evils  to  which 
impure  air  give  rise  are  invidious,  attack- 
ing the  weak  and  undermining  the  phys- 
ical system  of  both  weak  and  strong,  ren- 
dering them  more  susceptible  to  various 
forms  of  sickness,  notably  the  zymotic  or 
filth  diseases.  Thus  it  is  evident  that  no 
matter  how  much  the  nature  of  the  dan- 
gers from  this  source  may  have  been  mis- 
understood in  the  past  they  are  sufficiently 
grave  to  demand  all  reasonable  efforts  to 
ward  them  off.  The  first  aim  should  be  to 
prevent,  as  far  as  possible,  the  formation  of 
foul  air  within  the  sewers,  and  the  second 
to  keep  such  air  as  may  form  away  from 
mankind.  After  good  design  and  construc- 
tion of  the  sewer  conduits,  as  such,  have 
been  secured  ventilation  should  be  called 


74 

upon  for  the  introduction  of  a  plentiful  sup- 
ply of  fresh  air  and  the  removal  of 'foul 
air  to  points  where  it  will  be  diffused 
throughout  the  atmosphere  without  offense. 
Stagnation  of  air  within  the  sewers  must 
be  avoided. 

DR.  BILLINGS'   OPINIONS  ON  SEWER  AIR 
AND  VENTILATION. 

Before  leaving  this  subject  some  quota- 
tions may  be  introduced  to  advantage  from 
the  exhaustive  work  entitled  "Ventilation 
and  Heating,"  by. Dr.  John  S.  Billings, 
formerly  Siirgeon^General  U.  S.  A.,  and  a 
recognized  sanitary  authority.  Among 
other  things  Dr.  Billing's  says  : 

The  air  of  an  ordinary  modern,  fairly  well  con- 
structed and  ventilated  sewer  appears  to  differ 
from  the  street  air  chiefly  in  having  a  higher  pro- 
portion of  carbonic  acid. 

*  *  *  1C  *  * 

Specific  pathogenic  micro-organisms  have  not 
been  found  in  the  air  of  sewers  *  *  *  *  As 
regards  house  drains  and  soil  pipes,  the  condition 
cf  the  air  in  them  depends  greatly  upon  whether 
they  "are  properly  ventilated  or  not.  So  long  as 


75 


the  fixtures  connected  with  them  are  in  daily  use 
these  pipes  are  lined  with  a  moist  slimy  layer  of 
organic  matter,  in  which  bacteria  of  various  kinds 
grow  in  immense  numbers.  If  the  supply  of  air 
is  abundant,  these  bacteria  are  mostly  aerobic  and 
the  substances  produced  by  their  action  are,  as  a 
rule,  odorless  and  are  rapidly  carried  away,  by  the 
next  flush  of  liquid,  if  soluble. 

****** 
In  hospitals,  before  the  introduction  of  antisep- 
tic methods  of  treatment  of  wounds,  the  pyogenic 
organisms  were  of  course  very  numerous  in  the 
hospital  drains,  and  there  are  several  cases  in 
which  localized  outbreaks  of  erysipelas  and  un- 
healthy wound  action  appeared  to  be  connected 
with  the  passage  of  the  house  drain  air  into  the 
ward. 

****** 

Distinguished  English  sanitarians  believe  that 
typhoid  fever  has  been  spread  through  the  gases 
coming  from  foul  sewers,  but  I  know  of  no  satis- 
factory evidence  of  such  an  occurrence.  Diph- 
theria and  typhoid  fever  are  diseases  which  pre- 
vail more  extensively  where  there  are  no  sewers 
than  in  the  sewered  part  of  the  cities,  even  where 
the  sewers  are  badly  constructed. 

While  I  do  not  attach  much  importance  to  sewer 
air  as  a  means  of  transmission  of  specific  disease, 
I  believe  that  its  continuous  inhalation  is  dangerous, 
owing  to  the  large  amount  of  volatile  organic  mat- 


76 

ter  which  it  contains,  and  for  that  reason,  as  well 
as  to  prevent  the  formation  of  explosive  mixtures 
and  of  unpleasant  odors,  continuous  ventilation 
should  be  provided  for  all  sewers,  house  drains 
and  cesspools. 

In  well  constructed  sewers  Dr.  Billings 
considers  ventilation  an  easy  matter,  which 
can  generally  be  effected  by  frequent  open- 
ings to  the  outer  air,  and  always  at  each 
dead  end  of  a  sewer.  Special  tall  ventilat- 
ing shafts,  or  ventilation  through  factory 
furnaces  or  chimneys  he  considers  as  of  lit- 
tle value,  stating  that  the  influence  of  such 
shafts  or  chimneys  extends  only  to  the 
nearest  air  inlet. 

Ventilation  through  house  soil  pipes  is 
approved  where  the  sewers  and  house  con- 
nections are  properly  designed,  constructed 
and  operated,  and  all  are  under  the  con- 
trol of  the  municipal  engineer,  provided 
also  the  houses  on  a  given  street  are  nearly 
uniform  in  height.  Where  opposite  condi- 
tions prevail,  so  that  the  air  in  the  sewers 
is  bad,  and  the  tops  of  the  soil  pipes  of  one 
house  would  end  under  the  windows  of 
another,  the  Doctor  thinks  that  main  traps 


77 

should  be  placed  on  all  soil  pipes  and  air 
inlets  and  outlets  be  placed  on  the  sewers 
at  intervals  of  300  to  400  ft. 

FEATURES  PECULIAR   TO  THE    COMBINED 
SYSTEM. 

Coming  now  to  sewers  of  the  combined 
system  their  most  notable  differences 
from  separate  sanitary  sewers  are  their 
greater  size  and  the  use  of  catch  basins  or 
inlets  for  the  admission  of  surface  water. 
They  are  generally  of  brick,  stone,  or  con- 
crete, or  a  combination  of  two  or  more  of 
these,  instead  of  being  chiefly  of  vitrified 
pipe.  Still  another  distinctive  feature  is 
the  provision  of  storm  overflows,  by  means 
of  which  the  main  sewers,  when  over- 
charged at  times  of  heavy  rainfall,  may 
empty  a  part  of  their  contents  through  a 
short  conduit  into  some  water  course.  At 
such  times  the  sewage  is  diluted  by  the 
rain-water,  while  the  stream  which  re- 
ceives the  overflow  is  also  of  an  unusually 
large  vplume.  The  relief  thus  afforded  ren- 
ders possible  smaller  conduits  than  could 


78 


otherwise  be  used  without  backing  up  sew- 
age into  houses  or  flooding  streets  and 
cellars  on  the  lower  levels  of  the  city. 

SIZE,  SHAPE  AND  MATERIAL  OF  COMBINED 
SEWERS. 

The  actual  size  of  the  sewer  of  course 
depends  upon  local  conditions,  as  to  a  large 
extent  does  its  shape  and  material.  Where 
the  depth  of  flow  varies  greatly  it  is  de- 
sirable to  give  the  sewer  a  cross-section  de- 
signed to  suit  all  flows  as  fully  as  possible. 
Experience  has  shown  this  to  be  an  approx- 
imation to  the  cross-section  of  an  egg  plac- 
ed upright  on  its  smaller  end.  With  this 
section  a  maximum  depth  and  velocity  of 
sewage  is  secured  for  a  minimum  flow, 
rendering  deposits  and  stoppages  far  less 
liable.  With  sewers  having  a  flow  more 
nearly  constant  and  equal  to  their  full  cap- 
acity the  form  may  be  modified  to  that  of 
an  ellipse,  a  horse  shoe  with  an  arc  of  a 
circle  for  an  invert,  or  bottom,  a  circle, 
or  some  modification  or  combina- 
tion of  these,  according  to  circumstances. 
For  the  larger  sewers  brick  is  by  far  the 


most  common  material,  both  because  of 
its  cheapness  and  of  its  adaptability  to  any 
shape.  Stone  inverts  are  sometimes  em- 
ployed on  heavy  grades,  notably  where 
much  sand  is  carried  in  suspension,  in  or- 
der to  present  a  more  lasting  surface  to  the 
scouring  and  wearing  effect  of  gritty  ma- 
terial. Concrete  is  sometimes  used  for  in- 
verts, where  leakage  may  be  expected,  or 
in  material  liable  to  movement,  but  more 
commonly  it  affords  a  foundation  for  the 
brickwork.  The  concrete  is  also  sometimes 
extended  up  the  sides  of  the  sewer,  and 
sometimes  completely  around  it.*  If  the 
material  is  liable  to  much  settlement,  as  in 
marshes  and  bogs,  the  sewer  may  be  con- 
structed on  a  timber  platform,  the  latter 
sometimes  being  supported  by  piles,  gener- 
ally having  at  least  a  thin  layer  of  concrete 
between  it  and  the  invert. 

It  not  infrequently  occurs  that  sewers 
must  be  constructed  through  rock.  In  com- 
paratively rare  cases  this  is  sufficiently  solid 
to  warrant  the  use  of  an  unlined  tunnel, 
where  grades  are  sufficient  to  permit  a 

*  See  foot  note,  i>age  CO. 


80 

rough  surface.  But  generally  stones  and 
uneven  walls  left  after  blasting  make  lin- 
ing necessary,  which  is  commonly  com- 
posed of  brick,  with  any  spaces  behind  the 
ring  or  rings  filled  with  brick  or  stone 
masonry,  or  concrete. 

CATCH  BASINS  OB    RAINWATER  INLETS. 

A  catch  basin  is  generally  placed  at  each 
street  corner,  with  a  grated  opening,  or 
otherwise,  giving  the  surface  water  access 
to  a  chamber  or  basin  beneath  the  sidewalk, 
from  which  a  pipe  or  other  conduit  leads  to 
the  sewer.  Catch  basins  may  be  provided 
with  water  traps  to  prevent  the  sewer  air 
from  reaching  the  street,  but  these  traps 
are  liable  to  lose  their  seal  through  evapo- 
ration in  dry  weather,  unless  they  are  re- 
newed by  manual  labor  from  the  public 
water  supply  system.  To  prevent  the 
carrying  of  street  washings  into  the  sewers 
catch  basins  should  be  provided  with  silt 
chambers  of  considerable  depth  with  over- 
flow pipes  leading  to  the  sewers,  and  thus 
lessen  the  bulk  of  the  heavy  suspended 
matters  in  the  silt  chamber  to  be  removed 


81  " 


by  buckets  and  carted  away  at  proper  in- 
tervals. In  the  case  of  long  street  blocks 
catcli  basins  may  be  placed  in  the  centers 
of  the  blocks,  as  well  as  at  street  corners. 

STOEM  OVERFLOWS. 

Storm  overflows  are  simple  in  theory, 
and  often  so  in  construction,  the  main 
point  being  to  ensure  an  overflow  into 
another  conduit  when  the  flow  reaches  a 
certain  elevation  in  the  sewer.  Where 
main  and  intercepting  sewers  are  at  right 
angles  to  each  other  the  connection  is 
sometimes  so  made  that  the  dry  weather 
flow  drops  into  the  intercepting  sewer,  but 
the  flood  flow,  with  its  greater  volume  and 
velocity,  shoots  over  the  interceptor,  in 
part,  and  into  and  through  the  overflow 
sewers.  The  lower  portions  of  main  sewers 
formerly  discharging  at  many  points  into 
a  stream  or  lake  are  sometimes  utilized  in 
this  manner  when  intercepting  sewers  are 
added. 

The  junction  of  large  sewers,  and  other 
complications  in  combined  sewerage  sys- 
tems, sometimes  afford  ample  opportunity 


82 

for  the  engineer  and  contractor  in  design- 
ing and  building  masonry  suitable  for  such 
places. 

Sewers  designed  to  remove  surface  drain^ 
age  alone  are  practically  the  same  as  com- 
bined sewers,  without  house  connections, 
and  need  no  discussion  here. 

PUMPING    STATIONS,    RECEIVING    RESER- 
VOIRS AND  FORCE  MAINS. 

A  large  percentage  of  the  sewerage  sys- 
tems of  the  United  States  and  Canada 
operate  wholly  by  gravity,  but  it  is  some- 
times necessary  to  pump  a  part  or  all  of 
the  sewage  of  a  city.  The  lifts  involved 
are  usually  quite  low,  so  that  high-priced 
pumping  machinery  is  not  required.  It 
may  be  necessary  to  thoroughly  screen  the 
sewage  before  it  passes  to  the  pumps,  or  to 
provide  these  with  valves  not  likely  to  be 
injured  by  the  miscellaneous  bulky  sub- 
stances in  the  sewage. 

The  Shone  hydro-pneumatic  system,  used 
successfully  at  the  World's  Columbian 
Exposition  and  elsewhere  in  this  country 
and  abroad,  may  sometimes  be  used  to  lift 


83 


sewage  to  higher  levels.  In  this  system 
compressed  air  from  a  central  station  is 
automatically  discharged  into  a  receiving 
chamber  with  which  the  sewers  are  con- 
nected, whenever  the  chamber  fills  to  a 
certain  point.  The  air  under  pressure 
forces  the  sewage  through  the  outlet  pipe. 

Where  pumping  is  necessary  receiving 
reservoirs  with  more  or  less  storage  cap- 
acity may  sometimes  be  provided  with 
advantage,  to  equalize  the  work  demanded 
of  the  pumps  and  perhaps  to  permit  shut- 
ting down  the  pumping  plant  at  night. 
Such  reservoirs  are  generally  covered, 
unless  in  very  isolated  localties,  and  may 
be  ventilated  by  connecting  with  the 
smokestack,  or  the  gases  from  the  venti- 
lator may  be  conveyed  to  the  furnace  fire. 

Force  mains  are  generally  required  in 
connection  with  pumping  plants,  but  some- 
times the  latter  are  so  near  the  point  of 
outlet,  serving  as  mere  vertical  lifts,  that 
the  discharge  pipes  from  the  pumps  cut  no 
figure.  When  employed  the  force  main 
will  naturally  be  of  cast  iron,  similar  to 
that  for  a  water  supply  system. 


84 

TIDAL  CHAMBERS. 

Besides  receiving  and  storage  reservoirs 
at  pumping  stations  these  may  be  required 
where  the  disposal  of  sewage  is  into  tide 
water  under  such  conditions  that  it  is 
necessary  to  discharge  it  on  ebb  tides. 
The  main  distinguishing  features  of  such 
reservoirs,  as  compared  with  these  des- 
cribed above,  is  an  arrangement  of  gates 
which  will  permit  of  emptying  the  reser- 
voir in  a  brief  period.  These  gates  should 
be  easily  handled  in  order  to  reduce  the 
cost  of  attendance.  This  may  sometimes 
be  effected  by  mechanical  power  provided 
by  the  outflowing  sewage. 

FINAL  PLANS  AND  SPECIFICATIONS. 

Before  bids  for  construction  are  invited 
full  plans  and  specifications  should  be  pre- 
pared by  the  engineer.  The  plans  should 
be  in  sufficient  detail  to  make  the  general 
design  and  all  the  accessories  of  the  sys^ 
tern  perfectly  plain  to  bidders,  and  the 
specifications  should  be  explicit  upon  every 


85 

point  which  comes  within  their  scope. 
Blue  prints  of  the  plans  and  printed  copies 
of  the  specifications  should  be  ready  for 
all  inquiring  bidders  in  advance  of  the 
date  fixed  for  opening  bids.  The  specifi- 
cations are  usually  accompanied  with  the 
form  of  contract  to  be  executed  between 
the  city  and  the  successful  bidder.  In  the 
matter  of  specifications  and  forms  of  con- 
tract the  engineer  should  generally  work 
in  conjunction  with  an  able  lawyer,  the 
city's  permanent  legal  representative,  or 
otherwise,  according  to  circumstances. 
Years  of  experience  on  sewer  work  in  a 
particular  city  may  fit  an  engineer  to  cope 
single-handed  with  all  the  legal  questions 
involved,  but  in  the  long  run  co-operation 
with  members  of  the  legal  profession  will 
prove  advantageous.  When  difficulties 
with  contractors  arise  the  city's  legal  ad- 
viser is  pretty  sure  to  be  called  in,  so  it 
is  well  that  he  should  be  consulted  at  the 
start.  Outside  of  his  own  particular  city 
the  engineer  may  be  practically  helpless 
in  legal  matters,  owing  to  the  wide  di- 
vergence of  laws  relating  to  public  im- 


86 

provements    in    cities    of   the   same   and 
of  different  states.* 

SECURING  BIDS  AND  AWARDING  CONTRACTS. 

In  no  department  of  the  engineer's  work 
can  more  money  be  saved  his  employers 
than  in  the  securing  of  numerous  truly 
competitive  bids  from  able  contractors  and 
in  deciding  to  whom  the  contract  should 
be  awarded.  On  the  proper  performance 
of  these  duties  depends  not  only  the 
first  cost  of  the  improvements,  but  the 
interest  and  maintenance  account  and  to 
a  large  extent  the  successful  operation  of 
the  undertaking.  It  is  more  essential  to 
secure  an  able  and  honest  contractor  than 
a  low  bid;  more  important  that  the  work 
be  done  well  than  that  it  be  done  cheaply. 
The  number  and  character  of  the  bidders 
on  a  given  job  will  depend  upon  the  im- 
portance of  the  work,  the  publicity  given 
to  the  proposed  letting  and  the  character 

*  A  form  of  specification  and  contract  is  given  in  Staley  & 
Pierson's  ''Sepatate  System  of  Sewerage"  Prof.  J.  B. 
Johnson's  "  Engineering  Contracts  ai  d  Specifications  "  is  a 
valuable  book  devoted  exclusively  to  the  subjects  named  in 
its  title. 


8? 

of  the  plans,  specifications  and  foi-ms  of 
contract.  In  these  days  of  numerous  con- 
tractors eager  for  work  at  a  fair  price  it  is 
only  necessary  to  present  a  clear  idea  of 
the  work  to  be  done  and  just  conditions 
for  its  execution  to  secure  an  abundance  of 
proposals  on  almost  any  job,  provided 
only  the  opportunity  to  bid  be  brought 
to  the  attention  of  the  possible  bidders. 
Most  cities  and  towns  are  obliged  by  law 
to  advertise  all  contract  lettings  where 
more  than  a  small  cost  is  involved.  It  is 
generally  required  that  the  advertisements 
shall  appear  in  one  or  more  local  news- 
papers and  permissible  that  it  be  inserted 
in  others.  The  local  newspapers,  even  in 
the  large  cities,  reach  only  a  small  pro- 
portion of  possible  bidders,  almost  ex- 
clusively those  of  the  city  in  which  the 
papers  are  published.  For  this  reason, 
and  because  of  the  better  results  which  ex- 
perience teaches  are  to  be  secured  thereby, 
thv3  practice  of  advertising  engineering  con- 
tracts in  engineering  journals  is  rapidly 
growing  in  favor  of  late.  When  such  a 
course  is  pursued  the  work  in  hand  is 


brought  to  the  attention  of  the  contractors 
of  a  great  section  of  the  country,  or  of  the 
whole  country,  if  of  sufficient  importance, 
instead  of  to  those  of  one  city,  and  the 
number  of  bids  received  is  in  like  propor- 
tion. But  this  is  not  the  only  advantage. 
The  wider  competition  renders  far  more 
difficult,  yes,  practically  impossible,  ex- 
cept under  the  most  corrupt  city  govern- 
ments, the  growth  of  a  ring  of  local  con- 
tractors who  through  combinations,  per- 
sonal favoritisms  and  even  worse,  maintain 
prices  at  a  high  point,  at  the  same  time 
generally  doing  poor  work. 

The.  bids  having  been  received,  they 
should  be  referred  to  the  engineer  for  tab- 
ulation and  recommendation.  From  his 
estimates  of  quantities  he  can  determine  the 
relative  aggregate  prices  of  the  several 
bidders,  and  from  his  knowledge,  through 
acquaintance  and  inquiry,  of  the  bidders, 
and  of  the  probable  cost  of  the  work  in 
question,  he  can  decide  upon  and  report  the 
most  favorable  bid.  As  stated  above  this 
is  by  no  means  always  the  lowest  bidder, 
and  it  should  net  be  obligatory  upon  the 


89 

city  to  award  the  contract  to  the  parties 
who  offer  to  do  the  work  for  the  least 
money.  Unfortunately  the  experience  of 
many  cities  in  having  their  officials  award 
contracts  to  favored  bidders  has  led  to  leg- 
islative enactments  affecting  some  local- 
ities which  make  it  imperative  that  con- 
tracts shall  be  given  to  the  lowest  bidder, 
although  often  the  privilege  of  rejecting 
all  bids  and  readvertising  is  given.  This 
is  a  long  step  in  advance,  but  where  the 
officials  can  be  trusted  time  and  expense 
can  be  saved  both  city  and  contractor  by 
allowing  an  award  to  other  than  the  lowest 
bidder,  if  demanded  by  the  best  interests 
of  the  city,  based  on  past  records  of  con- 
tractors and  the  danger  of  poor  work  at  ex- 
cessively low  prices.  Such  a  course,  aside 
from  obliging  a  city  to  accept  an  undesir- 
able bid,  discourages  designing  contract- 
ors and  those  who,  in  their  eagerness  for 
work,  figure  too  low,  and  does  not  call 
upon  responsible  men,  of  good  judgment, 
to  be  to  the  trouble  and  expense  of  put- 
ting in  bids  the  second  time. 


90 


THE    PROPER    EXECUTION    OF   THE   CON- 
TRACT. 

The  contract  having  been  awarded  and 
construction  started,  it  devolves  upon  the 
engineer  to  give  the  contractor  all  neces- 
sary lines  and  grades,  and  any  information 
needed  and  not  provided  in  the  plans  and 
specifications.  It  is  also  his  duty,  both  per- 
sonally and  through  his  inspectors,  to  see 
that  the  work  is  done  according  to  the 
plans  and  specifications.  This  requires  the 
most  careful  and  conscientious  attention  on 
the  part  of  able  men.  Every  detail  of  con- 
struction must  be  watched  with  an  eagle 
eye  and  no  work  not  subject  to  complete 
examination  after  it  has  been  executed 
should  be  allowed  to  proceed  in  the  ab- 
sence of  the  inspectors.  On  pipe  work  or 
conduit  construction,  especially,  one  in- 
spector should  never  be  called  upon  to  look 
after  work  in  more  than  one  street  at  the 
same  time.  Pipe  and  brick  must  be  ex- 
amined with  the  greatest  care,  the  former 
piece  by  piece.  Cement  should  be  sub- 
jected to  proper  test  to  show  its  fitness  for 


01 


the  use  to  which  it  is  to  bo  put.  This  re- 
quires at  least  a  simple  testing  laboratory, 
and  the  provision  of  a  fully-equipped  one 
is  money  well  spent  where  naich  work  is  to 
be  done.  After  the  sewers  are  completed 
they  should  be  tested  for  obstructions,  the 
small  sewers  by  passing  a  ball  through,  or 
otherwise,  and  large  ones  by  having  a  man 
go  through  them. 

REGULATIONS  FOK    THE  USE    OF    SEWERS. 

These  include  all  necessary  precautions 
for  the  prevention  of  obstructions,  chief  of 
which,  perhaps,  is  the  proper  laying  and 
joining  to  the  street  sewer  of  house  con- 
nections. This  work  is  often,  if  not  gen- 
erally, done  by  plumbers,  but  all  such 
should  work  under  a  license,  revokable  for 
non-compliance  with  city  and  town  ordin- 
ances, and  should  be  under  the  supervision 
of  the  engineering,  sewer  or  health  de- 
partment. The  size,  grade  and  material  of 
house  connections  should  be  specified  in  the 
above  regulations,  and  in  order  that  pros- 
ecutions and  punishments  may  be  possible 
for  offenses  against  these  and  other  rules 


92 

it  is  necessary  to  have  an  ordinance  or  or. 
dinances  passed,  embodying  all  the  neces- 
sary rules  and  regulations  and  providing 
penalties-.* 

OPERATING  THE  SYSTEM. 

The  sewers  completed  their  operation  is 
nearly  always  very  simple,  especially  where 
pumping  or  purification  is  not  necessary. 
A  superintendent  of  sewers,  in  fact  if  not 
in  name,  is  generally  employed  to  have 
general  charge  of  the  sewerage  system. 
This  official  often  oversees  house  connec- 
tions and  frequently  has  charge  of  minor, 
and  sometimes  of  important  extensions  of 
the  system.  He  removes  stoppages  and 
looks  after  flush  tanks  and  other  devices 
for  keeping  the  sewers  clean.  If  pumps 
are  used  these  are  likely  to  be  in  sole 
charge  of  the  pumping  engineer>  although 
he  may  be  under  the  superintendent. 
Where  purification  is  employed  a  man  in- 
dependent of  the  superintendent  may  or 
may  not  have  charge.  All  purification 


*  A  model  ordinance  will  be  found  in  the  ' '  Separate  Sys- 
tem of  Sewerage. " 


93 

plants  should  be  under  the  immediate  di- 
rection of  the  most  competent  men  attain- 
able, within  reasonable  limits,  as  intelli- 
gence and  knowledge  are  absolutely  essen- 
tial to  their  continued,  and  often  to  their 
temporary  success.  Politics  and  political 
berths  should  be  kept  clear  of  this  depart- 
ment of  the  sewerage  system,  if  from  no 
other — it  should  be  from  all  parts. 

SEWERAGE  COMMITTEE,  BOARD  OF  PUBLIC 
WORKS  OR  CITY  COUNCIL. 

The  above  considerations  suggest  the 
question,  should  the  construction  and  oper- 
ation of  a  sewerage  system  be  entrusted  to 
a  sewerage  committee  entirely  independent 
of  other  departments  of  city  government,  to 
a  board  of  public  works  charged  with  other 
municipal  improvements  of  an  engineering 
character,  or  to  the  city  council  ?  The 
answer  to  this,  like  that  to  so  many  otln-r 
questions  already  raised  in  this  volume,  is 
that  local  conditions  often  determine  what 
is  best. 

It  is  interesting  to  note  that  English 
cities  and  towns,  as  ck-arly  shown  in  Dr. 


Albert  Shaw's  "  Municipal  Government  in 
Great  Britain,"  manage  in  an  admirable 
manner  practically  all  their  public  works 
through  their  city  councils  and  committees 
of  the  same,  always  relying,  however, 
upon  able  and  experienced  engineers  and 
others  for  technical  advice  and  the  details 
of  operation.  In  this  country  the  mistrust 
of  city  councils  has  been,  and  largely  is 
PO  great  that  the  first  thought  of  tax-pay- 
ers on  undertaking  the  installation  or  ex- 
tension of  some  important  public  work  is 
to  entrust  it  to  a  special  and  independent 
body  of  men. 

*-  The  English  system  has  the  advantage 
that  all  public  improvements  are  thereby 
carried  out  with  due  consideration  to  their 
relation  to  reSeh  other  and  to  the  finances 
of  the^ity  as  a  whole.  A  board  of  public 
works  entrusted  with  streets,  sewers,  water 
.  and  lighting  plants,  if  the  two  latter  be 
operated  by  the  city,  would  be  a  close  ap- 
proach to  the  English  plan,  and  would  in 
many  instances  have  its  advantages  over 
that  plan  under  American  conditions. 
Generally  speaking  independent  sewer 


95 


commissions,  if  only  composed  of  the 
right  men — and  it  is  this  which  counts 
more  than  any  system — have  built  and  are 
managing  sewerage  systems  with  good  re- 
sults in  this  country.  But  from  the  nature 
of  the  case  they  cannot  always  so  plan 
their  work,  for  instance,  as  to  interfere  as 
little  as  possible  with  good  street  pave- 
ments, because  they  have  no  control  over 
the  time  and  place  of  laying  such.  What- 
ever the  system,  an  able  city  engineer,  or 
engineer  of  the  sewer  department,  should 
be  given  the  practical  settlement  of  all  en- 
gineering questions. 

SEWAGE  PURIFICATION    IN    ITS    GENERAL 
ASPECTS. 

Having  treated  the  other  phases  of  the 
subject  as  fully  as  the  space  available  will 
permit,  there  remains  for  consideration  the 
important  matter  of  sewage  purification. 
This  has  been  reserved  to  the  last,  except 
for  the  incidental  references  to  it  already 
made,  because  it  is  quite  complete  in  itself 
and  demands  independent  handling.  The 
main  principles  of  sewerage  construction, 


96 


aside  from  disposal  works,  have  been  es- 
tablished for  many  years,  but  the  best 
means  of  rendering  sewage  fit  to  discharge 
into  water  courses  or  other  bodies  of  water 
not  suitable  for  the  reception  of  crude  sew- 
age are  problems  of  yesterday,  to-day  and 
even  of  the  future.  Enough  has  been 
settled,  however,  to  render  no  longer  valid 
the  plea  that  sewage  purification  is  as  yet 
in  too  experimental  a  stage  to  forbid  efforts 
in  that  direction.  We  know  to  a  certainty 
how  sewage  may  be  rendered  harmless. 
Further  knowledge  will  probably  be  in  the 
line  of  making  present  processes  do  more 
work  without  additional  cost.  The  facts 
are,  that  the  two  older  systems  of  sewage 
purification  now  in  use,  land  treatment 
and  chemical  precipitation,  were  practised 
for  many  years  in  a  blind  rule  o'thumb 
way,  and  often  with  good  results,  before 
their  fundamental  principles  were  dis- 
covered. Since  the  discovery  of  these 
principles,  or  natural  laws,  we  can  do 
nearly  always  what  formerly  was  done  only 
occasionally. 

Blood  pulsed   through  man's  veins   for 


97 

countless  centuries  before  Harvey  dis- 
covered the  law  of  circulation,  and  many 
maladies  incident  to  blood  and  circulation 
were  helped  or  healed  in  utter  ignorance 
of  the  law,  but  since  and  by  means  of  the 
discovery  what  a  revolution  there  has  been 
in  medicine  and  hygiene  !  We  look  for- 
ward to  more  progress  in  these  particulars, 
but  we  do  not  for  this  reason  hesitate  to 
avail  ourselves  of  all  that  has  been  accom- 
plished. But  this  is  exactly  what  some 
people  would  do  in  the  matter  of  sewage 
purification,  or  at  least  they  offer  as  an 
excuse  that  the  science  is  in  too  tentative  a 
stage  to  warrant  the  adoption  of  any  plan 
as  yet,  their  real  motive  too  often  being 
a  desire  to  keep  the  municipal  purse  strings 
pulled  tight. 

What  is  most  needed  now  is  not  new 
processes,  but  the  careful  carrying  out  of 
well-known  methods,  with  observations  on 
the  results  obtained  under  all  the  varying 
circumstances  which  naturally  arise  in 
different  localities  and  under  varying  con- 
ditions at  the  same  works.  We  have  a 
host  of  suggestive  and  many  conclusive 


deductions  drawn  from  careful  and  long- 
continued  experiments,  both  at  home  and 
abroad,  but  we  need,  particularly  in  Amer- 
ica, to  have  more  of  the  scientific  spirit 
and  method  which  have  made  the  labora- 
tory work  so  successful  applied  to  the 
daily  operation  and  study  of  actual  sew- 
age works.  Instead  of  caviling  at  the 
uncertainties  of  sewage  purification  those 
who  raise  questions  might  better  take  their 
turn  at  efforts  to  perfect,  simplify  and 
cheapen  the  already  admirable  processes 
now  available.  They  may  rest  assured 
that  the  worst  yet  attained  by  intelligent 
effort  along  the  new  lines  of  work  is 
infinitely  better  than  the  shameful  prostitu- 
tion of  streams  and  lakes  now  going  on 
throughout  this  broad  land,  a  marring  of 
the  beautiful  face  of  nature,  rendering 
limpid  waters  black  and  repugnant,  chang- 
ing their  refreshing  breezes  to  sickening 
odors,  while  life-giving  water  is  made  a 
death-dealing  poison,  and  all  through 
sewage  pollution. 

Before  taking  up  sewage  purification  in 
detail  it  will  be  well  to  consider  what  sew- 


age  is,  from  the  standpoint  of  the  chemist 
and  bacteriologist,  and  what  should  be 
expected  or  desired  in  the  way  of  its 
purification.  Sewage,  when  fresh,  and  as 
it  appears  at  the  mouth  of  an  outlet  sewer, 
is  generally  a  cloudy,  opaque  grey 
liquid,  with  some  large  particles  of  sus- 
pended matter  not  easily  broken  up  in 
transit,  as  orange  peels,  rags,  paper  and 
various  nondescript  articles  too  numerous 
to  mention.  It  very  often  has  a  faint, 
musty  odor,  and  in  both  looks  and  .smell 
is  sometimes  quite  comparable  with  the 
suds-water  of  family  laundry  work. 
Nearly  all  of  the  sewage  is  simply  water, 
the  total  solids  in  supsension  averaging 
perhaps  2  per  1,000,  of  which  a  half 
may  be  organic  matter.  It  is  this  1  part 
in  1,000  which  is  to  be  removed  or  so 
changed  in  character  as  ttfW 'rendered 
harmless. 

These  facts  regarding  the  composition 
of  sewage  are  far  different  from  the 
popular  conception,  which  pictures  a  vile 
mass,  indescribable  in  appearance  and  odor. 
Such  ideas  are  gained  in  part  from  the 


100 

known  contents  of  cesspools  and  from  im- 
properly constructed  and  neglected  sewers, 
but  they  arise  largely  in  vivid  imagina- 
tions. They  would  be  applicable  in  many 
respects  to  sewage  allowed  to  stagnate  and 
take  on  putrescible  decomposition,  as  hap- 
pens in  cesspools  and  obstructed  sewers,  or 
where  the  sewage  stands  on  the  surface  of 
poorly  graded  land  disposal  areas,  or 
accumulates  in  any  similar  manner  before 
being  purified. 

The  greatest  danger  from  sewage  is  in 
the  harmful  bacteria  which  it  conveys, 
but  even  these  are  not  to  be  feared  if  kept 
out  of  the  human  system,  to  which  they 
rarely  gain  access  except  through  water 
used  for  domestic  purposes  or  in  connection 
with  milk  supplies. 

Generally  speaking,  sewage  swarms  with 
bacteria,  engaged,  when  sufficient  oxygen 
is  present,  in  the  laudible  occupation  of 
converting  unstable  organic  matter  which 
might  become  offensive  into  fixed  mineral 
compounds  of  a  wholly  unobjectionable 
character.  These  plants  may  number 
millions  to  the  teaspoonful,  and  yet  be 


101 

wholly  invisible,  so  minute  are  the  organ- 
isms and  so  hidden  is  the  mighty  work  in 
which  they  are  engaged.  To  isolate  the 
harmful  from  the  harmless  with  certainty, 
if  at  all,  is  an  achievment  for  some  future 
Pasteur. 

The  organic  matter  and  the  bacteria  al- 
ways accompany  each  other.  If  all  the 
bacteria  should  be  removed  or  killed,  but 
some  of  the  organic  matter  remain,  an- 
other crop  of  microbes  would  develop  as 
if  by  magic  as  soon  as  seed  was  sown,  al- 
though the  renewal  of  disease  germs  in 
their  orginal  quantities  would  rarely,  if 
ever,  occur  except  from  a  source  the  same 
as  or  similar  to  the  original.  But,  remove 
all  the  organic  matter  and  all  the  bacteria 
food  is  gone— and  without  food  death 
comes  swiftly,  even  though  the  bacteria 
be  legions. 

From  the  above  it  may  be  inferred  that 
all  sewage  purification  processes  are  valu- 
able in  so  far  as  they  remove  or  change 
the  composition  of  organic  matter.  Mechan- 
ical straining,  sedimentation  and  chemical 
precipitation  are  largely  removal  processes, 


102 


while  septic  tanks,  broad  irrigation,  inter- 
mittcnt  filtration,  contact  beds  and  perco- 
lating filters  change  the  putrescible  organ- 
ic matter  into  stable  compounds. 

Either  form  of  land  treatment  may  be 
employed  where  practically  complete  puri- 
fication is  desired.  Straining  or  sedimen- 
tation will  remove  only  a  small  portion  of 
the  organic  matter.  Chemical  precipita- 
tion and  the  use  of  septic  tanks  will  do 
more,  but  must  be  supplemented  by  irri- 
gation or  intermittent  filtration  where  a 
high  degree  of  purity  is  required.  Con- 
tact beds  and  percolating  filters,  generally 
preceded  by  septic  tanks,  but  sometimes 
by  sedimentation  or  chemical  precipita- 
tion instead,  may  be  relied  upon  to  pro- 
duce a  non -putrescible  effluent  relatively 
free  from  suspended  matter,  but  generally 
high  in  bacteria.  Aeration  may  also  be 
be  called  in  to  supplement  other  processes, 
but  the  part  which  it  can  perform  is  far 
more  limited  than  is  supposed  by  many. 

The  object  of  sewage  purification,  then, 
being  the  removal  of  organic  matter,  and 
certain  modes  being  available  for  the 


103 


partial  or  complete  accomplishment  of 
this  end,  the  question  is,  which  is  the  most 
desirable  ?  Like  nearly  all  the  other  ques- 
tions which  have  arisen  in  the  course  of 
this  book,  and  like  most  other  questions  in 
engineering,  other  sciences  or  the  arts, 
there  is  no  one  answer.  The  degree  of 
purification  required  and  the  local  condi- 
tions which  make  one  system  cheaper  than 
another  in  construction  and  operation  all 
have  their  weight  in  selecting  a  system  of 
disposal. 

It  sometimes  happens  that  a  partial  re- 
moval of  the  organic  matter  contained  in 
sewage  is  ample,  in  which  case  the  20  to 
30  per  cent.,  more  or  less,  that  can  be 
accomplished  by  either  sedimentation  or 
straining  will  be  sufficient.  If  better  re- 
sults are  wanted  and  some  50  per  cent.,  or 
slightly  more,  of  purification  is  needed, 
the  sedimentation  may  be  accelerated  by 
the  use  of  certain  chemicals,  which  con- 
stitutes chemical  precipitation,  or  the  sep- 
tic tank  may  be  employed.  If  neither  of 
these  will  suffice,  the  effluent  from  either 
process,  or  in  fact  from  sedimentation  or 


104 


straining,  may  be  applied  to  a  sewage  farm, 
intermittent  filters,  contact  beds  or  perco- 
lating filters  ;  or  where  plenty  of  hii'd  is 
available,  all  previous  treatment  may  be 
dispensed  with  and  intermittent  filtration 
or  irrigation,  commonly  known  as  sewage 
farming,  or  a  combination  of  these  two 
land  processes,  may  be  brought  into  requi- 
sition to  do  all  the  work.  Obviously  where 
only  partial  purification  is  required  there 
may  be  a  wide  range  of  choice  between 
the  methods  named.* 

Although  the  object  of  sewage  treatment 
may  sometimes  be  the  removal  of  bacteria, 
the  chief  aspect  of  most  of  the  sewage 
works  now  in  operation  is  to  prevent  nuis- 
ances in  the  nature  of  foul  sights  or  odors. 
Where  public  water  supplies  are  involved 
the  aim  is  to  keep  the  sewage  out,  or  to 
purify  the  water,  or  both. 

SEDIMENTATION. 
This  is   effected   by   allowing  the   sus- 

*  See  "  The  Partial  Purification  cf  Sev  age,"  by  C<  1.  Geo. 
E  Waring,  Jr.,  Ewjin- ering  Aevsof  Jau.  4.  1894,  for  an  ei- 
t<-ndt  d  d.scussion  of  the  subject  named  in  the  title  just 
quoted. 


105 

pended  matters  to  settle  in  tanks.  The 
partially  clarified  liquid  is  drawn  off,  leav- 
ing the  solid  matter,  called  sludge,  at  the 
bottom  for  subsequent  disposal.  This  pro- 
cess, as  has  been  intimated,  is  akin  to 
chemical  precipitation,  so  the  shape  of  the 
tanks,  the  relative  merits  of  continuous 
and  intermittent  settlement  and  the  treat- 
ment of  the  sludge  will  be  taken  up  later 
on. 

Experiments  with  sedimentation  at  Law- 
rence, Mass.,  during  the  last  three  months 
of  1893,  indicated  a  subsidence  of  18.2  per 
cent,  of  the  albuminoid  ammonia  and  12  per 
cent,  of  the  bacteria  in  the  crude  sewage 
during  a  period  of  four  hours.  The  same 
experiments  in  1894  showed  a  much  better 
average  for  organic  matter,  as  measured 
by  the  albuminoid  ammonia,  but  about  the 
same  results  for  bacteria,  the  respective  fig- 
ures being  30  and  14.6  per  cent.  In  1895, 
there  were  removed  48  percent,  of  the  total 
albuminoid  ammonia,  and  31  percent,  bac- 
teria; in  1897,  about  35  per  cent,  of  each.* 

*  Reports  of  the  Massachusetts  State  Board  of  Health, 
1893,  p.  41,6,  f^r  1894,  p.  454,  1805,  p.  451,  and  1897,  p.  416. 


106 

These  experiments  were  discontinued  early 
tinned  early  in  1898. 

It  is  hard  to  imagine  conditions  in  actual 
practice  which  would  warrant  the  con- 
struction of  tanks  of  sufficient  capacity  to 
admit  of  four  hours  settlement  where  only 
a  30  to  40  per  cent,  removal  of  the  organic 
matter  could  be  expected.  With  smaller 
tanks  the  work  done  would  of  course  be 
less,  so  sedimentation  is  not  likely  to  be 
employed  except  where  a  small  amount  of 
purification  at  a  slight  expense  is  all  that 
is  needed. 

MECHANICAL  STRAINING. 

This  admits  of  a  great  variety  of  prac- 
tice, ranging  from  attempts  to  remove 
rags,  paper  and  other  large  substances  to 
an  approximation  to  intermittent  filtration. 
Wire  screens  or  filters  of  various  materials 
may  be  employed.  Generally  little  is  ac- 
complished, but  in  well-constructed  and 
operated  plants  screening  or  straining  may 
be  an  important  factor  in  the  purification 
effected.  As  a  preliminary  to  intermittent 
filtration,  coke  strainers,  or  thin  filter 


107 

were  used  at  Lawrence  during  the  last 
seven  months  of  1894,  removing  52.4  per 
cent,  of  the  albuminoid  ammonia  in  the 
original  sewage.*  These  beds  ranged  from 
IK  to  8  ins.  in  thickness  during  the  experi- 
ments, and  the  sewage  passed  them  at  an 
average  rate  of  about  345,000  gallons  a 
day  for  six  days  in  the  week.  A  depth  of 
6  ins.  of  coke  is  given  as  desirable  and  it 
is  estimated  that  when  straining  ordinary 
sewage  from  5  to  8  cu.  yds.  of  coke  would 
have  to  be  removed  per  1,000,000  gallons 
filtered. 

Mechanical  straining  through  coke  or 
sand  at  the  rates  named  might  perhaps 
more  properly  be  termed  continuous  rapid 
filtration.  Some  of  the  better  of  the  re- 
sults given  are  about  the  same  as  those 
secured  in  the  same  experiments  by  means 
of  chemical  precipitation,  using  1,000  Ibs. 
of  sulphate  of  alumina  per  1 ,000,000  gal- 

*  Keport  of  the  Massachusetts  State  Board  of  Health  for 
1894,  p.  455.  The  rep  rts  of  the  Massachusetts  State  Board 
of  Health  from  189t  to  19u2,  inclusive,  contain  accounts  of 
various  further  experiments  with  coke,  anthracite  and 
bituminous  coal  as  screens.  From  3  to  15  ins.  of  these  ma- 
terials, working  at  rates  of  1,000,000  gallons  a  day  and  up- 
vards,  r<  moved  from  32  to  62  per  cent,  of  the  total  album- 
incid  aii  iiionia. 


108 

Ions  of  sewage,  or  7  grains  per  gallon,  and 
allowing  four  hours  for  precipitation.  The 
mechanical  straining  usually  employed  is 
insignificant  in  results  compared  with  the 
above.  The  same  may  said  of  sedimen- 
tation. Both  processes  in  these  experi- 
ments, as  well  as  the  chemical  tests  carried 
on  simultaneously,  were  intended  to  facili- 
tate and  relieve  the  work  of  filter  beds. 

CHEMICAL  PRECIPITATION. 

Sedimentation  alone  removes  only  such 
suspended  matter  as  will  sink  by  its  own 
weight  during  the  comparatively  brief 
time  which  can  be  allowed  for  the  purpose. 
Some  of  the  lighter  matters  may  of  course 
be  carried  down  by  the  heavier  particles,but 
the  total  results  are  comparatively  small. 
If  the  process  could  be  continued  long 
enough,  practically  all  matters  in  suspension 
might  be  removed,  but  those  in  solution 
would  remain  and  putrefaction  might  be- 
gin in  the  sludge,  if  not  in  the  sewage 
undergoing  clarification.  By  adding  cer- 
tain substances  chemical  action  sets  in  and 
precipitation  occurs.  Some  of  the  organic 


109 


substances  are  brought  together  by  the 
formation  of  new  compounds,  and  as  they 
fall  in  flaky  masses  they  carry  with  them 
other  suspended  matter.  As  in  sedimen- 
tation or  straining,  a  part  of  the  bacteria 
are  removed  by  mere  entanglement,  while 
every  grain  of  organic  matter  removed 
decreases  by  so  much  the  bacterial  food 
supplies,  and  thus  the  potential  number  of 
bacteria, 

A  great  number  and  variety  of  chem- 
icals have  been  employed  as  precipitants, 
but  years  of  experience  have  resulted  in 
the  general  adoption  of  lime,  sulphate  of 
alumina  and  some  of  the  salts  of  iron, 
more  especially  ferrous  sulphate  or  cop- 
peras, or  a  combination  of  two  of  these,  as 
best  suited  for  the  chemical  precipitation 
of  sewage.  The  character  of  the  sewage 
and  the  relative  cost  of  the  several  chemi- 
cals in  a  given  locality  should  be  deter- 
mining factors.  Lime  is  cheap  almost 
everywhere,  but  the  comparatively  large 
quantities  required  increase  greatly  the 
amount  of  sludge.  Sulphate  of  alumina 
is  not  so  readily  obtained,  and  often  must 


110 

be  transported  such  a  distance  as  to  make 
freight  rates  quite  a  factor  in  its  cost.  It 
is  often  used  in  conjunction  with  lime, 
producing  a  less  amount  of  sludge  than 
lime  alone  and  in  some  cases  doing  more 
effective  work.  Where  either  an  acid 
sewage  or  one  containing  iron  salts  is  to 
be  treated,  lime  may  be  used  without  the 
sulphate  of  alumina  and  a  considerable 
saving  effected.  If  the  acid  or  iron  salts  are 
discharged  at  intervals  the  sewage  must  be 
tested  from  time  to  time  to  determine 
when  to  modify  the  amount  of  chemicals 
artificially  applied.  A  very  interesting 
example  of  this  sort  is  found  at  Worcester, 
Mass.,  where  large  quantities  of  acid  and 
iron  are  discharged  into  the  city  sewers 
from  manufacturing  establishments.* 

In  buying  chemicals  of  any  kind  great 
care  should  be  exercised  in  determining  the 
available  amount  of  the  active  agent,  as 
the  amount  of  calcium  oxide  in  lime,  or  of 
alumina  in  sulphate  of  alumina,  different 
products  varying  greatly  in  this  respect, 

»  See  Engineering  Xeu-ss,  No.  15.  1F90,  and  July  28, 1892  ; 
also  Rafter  and  Baker's  "  Sewage  Disposal  in  the  United 
States." 


Ill 


notably  the  lime  from  different  quarries 
and  kilns.* 

The  chemicals  should  be  added  to  and 
thoroughly  mixed  with  the  sewage  before 
the  latter  reaches  the  settling  tank.  The 
mixing  may  be  effected  in  nearly  all  cases 
by  projections  into  the  channel  leading  to 
the  tank,  called  baffle  plates. 

Experience  has  demonstrated  that  the 
tanks  should  be  long  and  narrow  j  and  that 
they  should  be  operated  on  the  continuous 
rather  than  the  intermittent  plan.  The 
width  of  the  tank  may  be,  say  one-fourth 
its  length.  In  the  continnous  plan  the 
sewage  is  constantly  flowing  into  one  part 
of  the  tank  and  discharging  from  another 
in  a  more  or  less  clarified  state.  In  the 
intermittent  system  a  tank  is  filled  and 
then  the  flow  turned  elsewhere,  allowing 
the  sewage  in  the  first  tank  to  come  to 
rest.  Where  the  continuous  plan  is  used 
'the  sewage  generally  flows  through  a  set 

*  For  tl  e  theory  of  the  actions  of  the  various  re-agents, 
the  qiiHulities  employed  and  their  costs,  both  in  experimen- 
tal and  practical  work,  see  Rafter  and  Baker's  "Sewage Dis- 
posal i:i  the  United  States."  Tl>e  brief  limits  rf  tl.i-»v  lume 
render!  i  possible  much  more  than  a  discuhsion  of  g.  neral 
principles;  detailed  ninires,  UDHCCOII  pam  d  by  ihn  data 
upon  \Nhieh  they  are  based,  am  apt  to  be  misleading. 


112 


of  tanks  without  change  of  gates  or  other 
interruption  until  one  compartment  needs 
cleaning.  This  compartment  being  cut  out 
and  left  to  itself  for  a  while,  the  clarified 
sewage  is  then  drawn  off  gradually  from 
the  top  through  a  hinged  pipe,  the  upper 
and  open  end  of  which  takes  sewage  from 
the  surface  on  opening  a  valve  in  the  hor- 
izontal portion  of  the  drain  pipe  beyond 
the  hinged  joint.  When  the  effluent  is 
decanted  to  the  top  of  the  deposited  sludge 
the  valve  just  mentioned  is  closed  and 
another  one,  in  the  sludge  pipe,  opened, 
allowing  the  sludge  to  flow  out,  or  to  be 
pumped  out  for  final  disposition.  The 
tank  should  then  be  thoroughly  cleaned, 
after  which  it  may  be  treated  with  disin- 
fectants or  deodorants,  if  desired,  before 
being  again  put  in  use. 

The  disposition  of  sludge  is  one  of  the 
most  vexed  problems  connected  with  sew- 
age disposal.  It  is  a  pasty,  semi-liquid 
mass,  ordinarily  containing  from  90  to  95 
per  cent,  of  water  and  10  to  5  per  cent,  of 
solid  matter.  The  most  common  method 
of  disposal,  and  perhaps  the  one  most  gen- 


113 


erally  available  and  satisfactory,  is  to 
squeeze  as  much  water  as  is  possible  out 
of  the  sludge  by  means  of  presses  designed 
for  the  work.  This  greatly  reduces  the 
bulk  of  the  material.  The  liquid  from  the 
press  goes  back  to  the  tank  for  further 
treatment.  The  sludge  cake,  as  it  is  called, 
may  be  handled  easily.  It  is  sometimes 
burned  and  sometimes  hauled  away  by 
farmers  for  use  as  a  fertilizer.  There  have 
been  great  expectations  on  the  part  of  pro- 
jectors of  chemical  precipitation  works 
that  the  farmers  would  vie  with  each  other 
in  securing  the  sludge,  and  even  pay  good 
money  for  it.  The  general  experience, 
both  in  this  country  and  abroad,  has  been 
that  a  city  is  lucky  if  it  is  able  to  induce 
anyone  to  haul  the  sludge  away  for  it. 

In  some  cases  peat  or  some  other  absor- 
bent is  mixed  with  the  sludge  to  render  it 
more  easily  handled  and  removed  in, bulk. 
Again,  it  is  run  out  on  the  surface  of  coarse 
sand  and  gravel  beds  and  its  liquid  parts 
reduced  by  draining  and  drying.  Some  of 
the  difficulties  connected  with  this  last 
method  are  : 


114 

(1)  In  wet  weather  little  drying  takes 
place,  and  during  the  colder  mouths  the 
sludge  accumulates  in  considerable  quan- 
tities. (2)  Manual  labor  must  be  em- 
ployed to  remove  the  sludge  from  the 
draining  and  drying  beds.  (3)  Where 
chemical  precipitation  is  employed  suitable 
land,  in  character  and  extent,  is  often  not 
to  be  had. 

At  Birmingham,  England,  large  volumes 
of  sludge  are  pumped  through  force  mains 
distributed  through  portable  pipes  to 
and  covered  with  earth. 

There  remains  another  method  available 
for  some  seaside  cities,  and  that  is  dump- 
ing in  the  ocean  by  means  of  large  steam 
sludge  ships.  Thousands  upon  thousands 
of  tons  are  so  disposed  of  from  the  sewage 
works  of  London  and  Manchester,  Eng- 
land, and  Glasgow,  Scotland. 

The  capacity  of  the  settling  tanks  is 
often  the  chief  factor  in  determining  the 
cost  of  installing  precipitation  works.  As- 
suming that  the  sewage  should  be  one  hour 
in  passage  through  the  tanks,  and  that  the 
maximum  flow  is  twice  the  average,  pro- 


115 


vision  must  be  made  for  one-twelfth  the  to- 
tal daily  flow,  where  house  sewage  only  is 
treated.  This  makes  no  allowance  for  throw- 
ing out  a  portion  of  the  tanks  for  cleaning 
or  repairs.  It  would  certainly  be  erring 
on  the  safe  side,  if  at  all,  to  provide  a  tank 
capacity  equal  to  one-eighth  the  total  max- 
imum daily  flow.  Where  sewage  from  a 
combined  system  is  treated,  it  is  of  course 
practically  impossible  to  provide  a  tank 
capacity  sufficiently  large  to  treat  all  the 
sewage.  Either  the  excess  of  storm  water 
must  be  discharged  into  natural  water 
courses  along  the  lines  of  the  sewers  or 
pass  by  the  works  without  treatment.  If 
ample  tank  capacity  is  available  it  may  be 
possible  to  treat  all  the  sewage  during  the 
first  part  of  a  moderate  rain.  This  would 
mean  the  purification  of  the  foulest  portion 
of  street  and  other  washings,  after  which 
in  many  localities  it  might  be  admissible 
to  forego  all  attempts  at  purifying  the 
sewage,  as  the  results  which  could  be  ob- 
tained would  be  comparatively  insignifi- 
cant. During  such  a  heavy  rainfall  the 
sewage  of  a  combined  system  would  be 


116 

many  times  diluted,  and  where  the  effluent 
from  the  works  discharges  into  a  stream 
the  latter  is  also  greatly  increased  in  vol- 
ume. It  is  evident  that  where  purification 
is  proposed  in  connection  with  a  new  sew- 
erage system  the  separate  plan  will  prac- 
tically always  be  adopted.  Most  purifica- 
tion plants  in  this  country  have  been  built 
at  the  same  time  as  the  collecting  system, 
and  in  such  cases  the  separate  plan  has 
been  used.  Worcester,  Mass.,  was  forced 
to  adopt  purification  after  many  miles  of 
combined  sewers  had  been  built,  and  after 
it  had  converted  a  brook  with  a  consider- 
able drainage  area  into  an  outlet  sewer. 
Its  later  sewers  have  been  built  for  house 
wastes  only,  and  hundreds  of  thousands  of 
dollars  have  been  spent  since  the  sewage 
works  were  built  in  excluding  surface 
water  from  the  sewers. 

THE  SEPTIC  TANK. 

The  septic  tank,  as  we  now  know  it,  has 
been  developed  since  1894.  In  effect,  it  is 
a  sedimentation  basin,  so  designed  and 
operated  as  to  lessen  the  sludge  deposit  by 


II1 


dissolving  a  portion  of  it  and  by  reducing 
another  portion  to  gaseous  form.     This  re- 
duction  or  hydrolysis   of    the   sludge   is 
brought  about  by  anaerobic  bacteria,  which 
work  in  the  absence  of  air,  and  are  thus 
directly  opposed  in  character  to  the  aero- 
bic bacteria  or  nitrifying  organism  of  sew- 
age farms,  intermittent  filters,  contact  beds 
and   percolating   filters.     Since   inorganic 
matter  is  not  acted  upon  by  the  bacteria, 
its  exclusion  from  the  septic  tank  is  desir- 
able.  To  this  end,  small  grit  chambers  are 
provided,  through  which  the  sewage  passes 
on  its  way  to  the  septic  tank.     The  high 
specific  gravity  of  the  sand  and  other  min- 
eral matter  in  the  sewage  causes  much  of 
it  to  sink  in  a  brief  period  of  time,  while 
the  remainder  of  the  suspended  matter,  in- 
cluding the  lighter  organic  sludge,  passes 
into  the  septic  tank.     Since  the  admission 
of  air  to  the  septic  tank  would  tend  to  dis- 
place  the   anaerobic  bacteria  by  aerobic, 
the  tank  inlets  and  outlets  are  generally 
submerged  a  foot  or  so  beneath  the  normal 
sewage  level.     The  tanks  are  made  long 
and  narrow,  thus  affording  time  for  sedi- 


118 


mentation,  and  have  a  sewage  depth  of  6 
to  9  feet.  For  convenience  in  removing 
sludge,  their  bottoms  slope  to  one  or  more 
sumps  or  gates. 

Whether  or  not  septic  tanks  should  be 
covered  has  not  been  universally  agreed. 
It  is  held  by  some  that  a  roof,  excluding 
light  and  air,  is  a  great  help,  if  not  a  ne- 
cessity, to  the  highest  efficiency;  while 
others  argue  that  roofing  is  unnecessary 
to  full  bacterial  action,  except  in  very  cold 
climates,  and  that  a  roof  need  be  provided, 
if  at  all,  only  for  such  tanks  as  are  near 
dwellings  or  much-traveled  highways,  and 
which  on  that  account  might  give  offense 
to  residents  or  passers  by. 

Any  fairly  water-tight  material  may  be 
used  in  constructing  septic  tanks ;  probably 
concrete,  either  plain  or  reinforced,  is  now 
used  more  commonly  than  any  other  ma- 
terial. The  roof,  as  well  as  the  walls  and 
bottom,  may  be  of  concrete,  or  where  low 
first  cost  is  an  object,  wood  may  be  used 
for  roofing. 

Since  the  action  of  the  septic  tank  is  due 
tc  anaerobic  bacteria,  while  further  purifi- 


119 


cation  is  effected  by  aerobic  germs,  and 
since  the  septic  effluent  is  not  only  high  in 
anaerobic  germ  contents,  and  nearly  if  not 
quite  without  available  oxygen,  the  septic 
effluent  is  sometimes  aerated  before  being 
passed  to  filter  beds.  Weirs  over  which 
the  effluent  flows  in  a  very  shallow  stream 
or  a  series  of  overflow  steps  are  used  for 
purposes  of  aeration. 

The  amount  of  sludge  removed  by  septic 
tanks  cannot  yet  be  safely  predicted  for  a 
given  sewage  works  until  actual  tests  have 
been  made.  Such  figures  as  are  available 
show  wide  variations  at  different  localities. 
No  one  should  be  deluded  by  observations 
of  the  amount  of  sludge  remaining  in  a 
septic  tank,  since  large  volumes  of  sludge 
in  a  finely  divided  state  may  pass  off  in 
the  effluent.  Volume  for  volume,  however, 
this  finely  divided  suspended  matter  will 
make  far  less  trouble  than  the  sludge  from 
ordinary  settling  tanks  or  from  chemical 
precipitation  works.  Some  of  it  is  already 
a  mineral  ash,  subject  to  no  further  organic 
change,  and  the  balance  is  partly  reduced 


120 

to  mineral  matter  and  also  to  food  for  the 
low  forms  of  organic  life. 

Such  sludge  as  remains  in  septic  tanks 
may  be  disposed  of  by  the  means  already 
described. 

In  some  cases,  probably  due  to  the  char- 
acter of  the  sewage  or  to  improper  opera- 
tion, sludge  from  septic  tanks  is  offensive 
when  first  exposed  to  the  air.  Under  such 
a  condition  the  sludge  disposal  should  be 
carried  on  at  a  remote  point,  or  the  sludge 
should  •  be  buried  quickly  a  few  inches 
beneath  the  earth.  Investigations  should 
also  be  made  to  determine  whether  the 
odors  cannot  be  prevented  by  a  change  in 
the  design  or  operation  of  the  tank. 

Were  it  within  the  scope  of  this  book, 
and  less  free  from  conflicting  claims,  it 
would  be  interesting  to  attempt  to  trace 
the  history  of  the  septic  tank.  The  sub- 
ject involves  claimants  in  Great  Britain, 
the  United  States,  Germany  and  France; 
and  also  many  early  tanks  installed  and 
used  with  success,  though  with  little  or  no 
understanding  of  the  principles  involved, 
long  before  the  name  septic  tank  came  into 


121 


use.  It  is  now  generally  recognized  that 
the  man  who  gave  the  septic  tank  its  name 
and  brought  it  into  scientific  prominence 
was  Donald  Cameron,  of  Exeter,  England, 
but  up  to  early  in  the  year  1905  it  was  not 
generally  conceded  that  Cameron's  work 
entitled  him  to  patent  control  of  the  septic 
tank  process.  The  question  was  then  in 
the  courts  of  the  United  States  for  trial, 
but  had  never  been  legally  raised  in  Great 
Britain,  so  far  as  the  author  of  this  book 
could  learn. 


ARTIFICIAL    AERATION.  —  "  ELECTRICAL  " 
PROCESSES. 

While  the  oxygen  of  the  atmosphere 
may  be  made  one  of  the  greatest  agents  in 
purifying  sewage,  some  writers  and  others 
have  laid  too  much  stress  upon  the  value 
of  artificial  aeration.  Mountain  streams, 
which  tumble  over  rocky  beds,  are  noted 
for  their  purity,  and  this  has  been  attributed 
largely  to  the  aeration  which  the  water 
receives.  It  should  be  remembered  that 


122 

the  waters  of  such  streams  are  generally  of 
a  high  degree  of  purity  to  start  with,  often 
being  little  different  from  rainwater  just 
from  the  clouds,  and  that  the  aerating 
process  is  quite  commonly  a  long  one.  It 
has  been  further  observed  that  even  badly 
polluted  streams  show  greatly  improved 
chemical  analyses  at  points  a  number  of 
miles  below  the  source  of  contamination. 
But  here,  sedimentation,  and  the  action  of 
both  animal  and  vegetable  life  in  their 
more  minute  forms,  play  a  notable  part  in 
the  purification  process,  and  the  time- 
element  is  also  important. 

It  has  been  well  established  by  the 
Massachusetts  State  Board  of  Health  in 
its  Lawrence  work  that  the  two  essentials 
for  the  removal  or  transformation  of  the 
organic  matter  in  sewage  are  oxygen  and 
time,  where  dependence  is  placed  on  a 
nitrifying  or  oxidizing  process.  The  time-' 
element  has  been  largely  ignored  by  some 
theorists,  a  few  of  whom  have  put  their 
theories  into  practice.  Purification  plants 
have  been  built,  and  more  have  been  projec- 
ted, in  which  the  great  reliance  has  been  put 


123 

upon  artificial  aeration,  either  by  forcing 
air  into  the  sewage  or  by  causing  the 
latter  to  fall  through  the  air  in  drops  or 
streamlets.  This  has  been  accompanied 
by  rapid  filtration,  generally  through 
sand.  Now  aeration  of  the  sewage,  or  of 
the  filtering  material,  may  be  employed  as 
an  aid  to  sewage  purification,  but  like  all 
things  else  it  has  its  limits.  It  can  main- 
tain a  supply  of  oxygen  which  is  of  use  up 
to  a  certain  point  and  this  will  be  of  value. 
All  in  excess  of  this  amount  is  of  no 
value,  and  even  this  is  not  of  use 
unless  time  is  given  for  the  action  of  the 
oxygen  and  of  the  nitrifying  organism. 
The  latter  develops  rapidly  in  the  presence 
of  oxygen  and  organic  matter,  transform- 
ing the  latter  into  mineral  compounds. 
These  facts  are  overlooked  by  some  of  the 
promoters  o.f  aerating  processes,the  assump- 
tion seeming  to  be  that  given  a  plenty  of 
air  the  desired  work  will  be  accomplished 
.almost  instantly.  The  facts  are  that  sew- 
age soon  loses  all  the  available  oxygen 
taken  up  by  it  during  aeration  and  needs 
to  be  aerated  again  and  again  until  all 


124 

the  organic  matter  is  transformed.  The 
time-element  can  best  be  secured,  almost 
invariably  in  some  form  of  filter  bed. 

Perhaps  there  is  an  even  greater 
misunderstanding  regarding  so-called 
electrical  methods  of  sewage  purifi- 
cation. These  processes,  which  have 
met  with  but  little  favor,  simply  pre- 
pare by  electrical  means  some  chemical 
agent  which  performs  all  the  work  accom- 
plished and  might  be  obtained  in  some 
other  manner,  although  possibly  at  greater 
expense.  In  the  Woolf  and  Hermite  pro- 
cesses either  sea  water  or  a  solution  of 
common  salt,  according  to  the  readiness  of 
obtaining  one  or  the  other,  is  partially  de- 
composed by  an  electric  current,  and  sodium 
hypochlorite  is  formed.  The  solution  is 
mixed  with  the  sewage  and  acts  as  a  deo- 
dorizer and  germicide,  its  efficiency  de- 
pending on  its  strength.  The  organic 
matter  remains  in  the  sewage  and  is  sub- 
ject to  secondary  decomposition  later  on. 
The  product  obtained  by  this  process 
might  be  of  value  under  certain  conditions, 


125 


the  same  as  other  good  disinfectants  are, 
but  there  seems  to  be  no  reliable  inform- 
ation to  show  that  anything  further 
can  be  expected  of  it. 

The  direct  treatment  of  sewage  by  elec- 
tricity has  been  talked  of  for  some  time 
but  it  still  remains  a  dream. 

BROAD  IRRIGATION  OR  SEWAGE  FARMING. 

Where  sewage  is  applied  to  the  surface 
of  the  ground  upon  which  crops  are  raised 
the  process  is  called  broad  irrigation,  or 
sewage  farming.  The  practice  is  in  most 
respects  similar  to  the  ordinary  irrigation 
of  crops  with  clean  water,  the  sewage  be- 
ing applied  by  a  variety  of  methods,  ac- 
cording to  topographical  and  other  natural 
conditions  and  the  kind  of  crops  under 
cultivation. 

The  land  employed  for  this  method  of 
purification  should  preferably  be  composed 
of  a  fairly  light,  porous  soil.  The  crops 
should  be  such  as  require,  or  at  least 
develop  best  under  a  large  amount  of 


126 


moisture.  Where  the  soil  is  heavy  and 
wc-t,  and  the  crops  cannot  stand  much 
water,  the  sewage  must  be  applied  spar- 
ingly, and  so  a  large  amount  of  land 
and  much  labor  must  be  provided.  As 
broad  irrigation  areas  may  be  prepared  at 
comparatively  small  expense  it  is  some- 
times feasible  to  make  use  of  land  not  so 
well  suited  to  the  purpose  as  might  be 
desired,  provided  it  can  be  obtained 
cheaply  enough  and  too  much  stress  is 
not  laid  upon  the  raising  of  crops.  The 
less  the  attention  paid  to  cropping,  gene- 
rally speaking,  the  greater  the  amount  of 
sewage  which  can  be  put  on  a  given  area 
of  land.  Wet,  clayey  soils  can  take  but 
little  sewage  under  any  circumstances, 
but  sometimes  improve  with  cultivation 
and  the  application  of  sewage. 

The  application  of  an  average  of  from 
5,000  to  10,000  gallons  of  sewage  per  day 
to  one  acre  of  land  is  considered  by  many 
as  a  liberal  allowance.  On  the  basis 
of  100  gallons  of  sewage  per  head  of 
population  this  means  that  one  acre  of 


127 

land  is,  sufficient  for  a  population  of  from 
50  to  100  persons.  More  could  be  purified 
if  the  crops  would  stand  it,  but  for  each 
kind  there  is  a  limit  which  if  passed 
means  the  destruction  of  the  crop. 

Allowing  even  10,000  gallons  of  sewage, 
or  100  persons,  to  an  acre  in  a  city  of  20,000 
inhabitants  would  require  200  acres.  To 
find  suitable  land  at  a  low  price  near 
cities  is  not  always  easy.  The  larger  the 
city  the  greater  the  difficulty.  Labor,  too, 
is  a  big  item  in  sewage  farming  on  this 
side  the  Atlantic,  especially  near  cities. 
As  a  partial  offset  to  this,  great  cities 
afford  excellent  and  never-failing  markets. 
Another  great  obstacle  to  adequate  finan- 
cial returns  from  sewage  farming  in 
America  is  the  deplorable  fact  that 
political  ends  and  not  business  principles 
govern  in  large  numbers  of  our  cities, 
though  there  is  good  reason  to  predict 
a  great  change  in  this  respect  ere 
long.  Where  such  conditions  do  prevail, 
however,  the  positions  of  both  superin- 
tendents and  laborers  on  sewage  farms  are 
ulinost  sure  to  be  considered  rewards  for 


128 

and  encouragements  to  party  service,  with 
results  most  unfavorable  to  the  enterprise 
in  hand.  Sewage  farming  means  the  sell- 
ing as  well  as  the  raising  of  crops,  and 
perhaps  of  live  stock,  and  so  requires 
business  ability  and  agricultural  skill. 
The  latter  must  be  accompanied  with  the 
faculty  of  handling  considerable  bodies  of 
men. 

These  apparently  discouraging  state- 
ments are  meant  rather  as  warnings.  They 
are  necessary  because  of  the  glowing  repre- 
sentations which  have  been  made  regard- 
ing the  profits  of  sewage  farming  by  those 
who  have  not  looked  at  all  sides  of  the 
question.  I  am  not  unmindful  of  the  re- 
sults of  sewage  farming  abroad,  but  Euro- 
pean conditions  are  far  different  from  ours. 
Many  of  the  European  farms  are  most  ad- 
miral ly  managed,  both  from  an  agricul- 
tural and  business  standpoint,  and  not  a 
few  of  them  have  to  contend  with  soil 
far  less  favorable  than  could  be  found 
in  many  sections  of  the  United  States. 
I  do  not  say  that  an  American  city  could 
not  conduct  so  great  an  enterprise  in  a 


129 


creditable  manner,  for  we  have  many 
well-conceived  and  well-operated  munici- 
pal works  of  great  magnitude.  I  do  say 
that  high  prices  for  land  near  large  cities, 
costly  labor,  a  constant  warfare  against 
corruption  with  too  frequent  surrenders, 
and  our  sudden  and  complete  changes  in 
government  all  make  sewage  farming  more 
difficult  here  than  abroad. 

For  the  present,  sewage  disposal  cannot 
be  accomplished  in  this  country  at  a  profit. 
It  is  sometimes  possible  to  regain  through 
the  raising  of  crops  a  part  of  the  expense 
entailed  in  removing  and  purifying  sewage, 
and  this  is  the  only  method  by  which  any 
considerable  portion  of  the  expense  has  yet 
been  recovered  here  or  elsewhere.  We 
should  be  thankful  for  the  day  of  small 
things,  and  wherever  a  revenue  can  be  ob- 
tained from  irrigation  area  or  filtration 
beds  our  efforts  should  be  to  secure  it.  But 
the  logic  of  figures  will  often  show  that 
some  method  of  disposal  that  carries  with 
it  no  financial  returns  is  the  cheapest,  in 
which  case  instead  of  crying  over  spilt  and 
wasted  sewage,  we  may  laugh  over  a  sav- 


130 

ing  in  capital,  interest  and  maintenance. 
Wherever  irrigation,  pure  and  simple, 
that  is  the  application  of  water  to  crops 
for  the  sake  of  moisture,  can  be  practiced 
to  advantage,  sewage  farming  should  re- 
ceive serious  consideration,  for  in  such 
localities  every  drop  of  water  is  valua- 
ble. As  ordinary  irrigation  may  yet  be 
used  in  the  East  as  well  as  in  the  West, 
(it  is  already  practiced  to  some  extent  in 
the  South)  the  use  of  sewage  for  mere 
watering  as  well  as  fertilizing  may  some 
day  be  seen -here  and  there  throughout  the 
length  and  breadth  of  the  land.  This  is  a 
subject  which  demands  careful  investiga- 
tion and  perhaps  might  be  taken  up  with 
advantage  by  some  of  our  agricultural  ex- 
periment stations  and  by  any  live  official 
in  a  position  to  do  so.* 

*  For  an  article  on  "The  Use  of  Sewage  for'  Iriigation  in 
the  \\  est "  ste  Angineei  ing  iYe«w  for  .Nov.  3,  Ife9j  ;  the  sub- 
stance of  the  article  is  a.so  given  in  Kafter  and  Baker's 
"  Sewage  Disposal  in  the  United  States.1'  A  later  treatment 
of  the  subject  may  be  found  in  "Sewage  Irrigation,"  Nos. 
3  and  22  of  Water  Supply  und  Irrigation  Papers  of  the  U.  fc. 
Geological  Survey,  by  Gto  W.  Rafter,  M.  Am.  Soc.  C.  E. 
In  March,  1905,  the  author  cf  this  book  visited  the  sewage 
farm  of  Pasadena,  Cal.,  and  also  land  to  which  some  of  the 
sewage  of  Los  Angeles  is  applied.  As  a  result,  he  is  more 
than  even  convinced  of  the  wisdom  of  using  sewage  for  ir- 
rigation wherever  water  is  scarce. 


131 


SUB-SURFACE  IRRIGATION. 

Before  passing  on  to  intermittent  fil- 
tration a  word  should  be  said  regarding 
sub-surface  irrigation.  The  system  is  cap- 
able of  use  on  a  small  scale,  chiefly  for 
private  dwellings,  various  public  institu- 
tions and  small  communities  where  for  any 
reason  surface  disposal  would  be  objection- 
able. Tiie  sewage  is  distributed  through 
agricultural  drain  tiles,  laid  with  open 
joints,  and  placed  only  a  few  inches  below 
the  surface.  Provision  should  be  made 
for  changing  the  disposal  area  as  often  as 
the  soil  may  require  by  turning  the  sewage 
into  sub-divisions  of  the  distributing  pipes. 
The  sewage  is  generally  discharged  auto- 
matically at  intervals  on  the  filling  of  a 
tank  to  a  certain  height.  Where  surface 
application  can  be  practiced  it  would  gen- 
erally, if  not  always,  be  preferable  to  this 
system. 

INTERMITTENT  FILTRATION. 

This  method  of   sewage  purification  is 
capable  of  producing  the  highest  results 


132 


under  favorable  conditions,  and  those  con- 
ditions prevail  perhaps  more  widely  in  this 
country  than  like  ones  for  any  other  sys- 
tem. 

The  process  is  a  most  simple  one. 
With  a  competent  man  in  charge  large 
areas  of  beds  can  be  operated  with  cheap 
labor.  The  construction  of  the  beds  is 
nearly  as  simple  as  their  operation,  only 
common  labor  being  required,  except  for 
putting  down  pipe  and  accessories. 

The  essential  features  of  filter  beds  are 
some  4  to  5  feet  of  medium-sized  sand, 
located  above  the  natural  ground  water 
level;  a  pipe  system  for  distributing  the 
sewage  to  one  or  more  points  on  each  bed, 
and  another  beneath  the  bed,  for  collecting 
the  purified  liquid.  In  operation,  the  sew- 
age is  turned  on  to  one  bed  for  a  given 
length  of  time,  and  then  to  another,  in 
order  to  give  the  first  a  rest,  or  literally  a 
breathing  spell.  When  the  beds  become 
clogged  with  the  matter  retained  on  their 
surface  and  in  their  uppermost  part,  they 
may  be  raked  over,  or  the  sludge,  and  with 
it  a  thin  layer  of  sand,  may  be  scraped  off. 


133 

If  the  beds  are  scraped,  it  will  eventually 
be  necessary  to  make  good  the  sand  re- 
moved, although  this  will  not  be  required 
until  perhaps  a  foot  has  been  taken  off, 
which  should  not  result  for  a  long  time. 

Intermittent  filtration  is  a  nitrifying 
process  effected  through  the  agency  of  ox- 
ygen and  bacteria,  and  requiring  time  for 
these  two  factors  to  act.  A  more  complete 
definition  is  perhaps  that  given  in  the 
Report  of  the  Massachusetts  State  Board 
of  Health  for  1893,  as  follows: 

The  process  *  *  *  consists  of  intermingling 
the  sewage  in  the  pores  of  the  filtering  material, 
with  sufficient  air  for  a  sufficient  time,  in  the  pres- 
ence of  micro-organisms  which  quickly  establish 
themselves  there. 

Experience  has  taught  that  a  good  filter- 
ing material  is  one  composed  of  clean, 
sharp  sand  with  grains  of  uniform  size, 
and  having  interstices  forming  about  one- 
third  the  total  volume.  The  interstices 
serve  as  air  spaces.  When  the  sewage  is 
admitted  to  the  sand  not  all  the  air  is 
driven  out,  and  hence  thtre  is  a  store  of 
oxygen  to  be  drawn  upon  by  the  bacteria* 


134 

As  more  and  more  sewage  is  added  the 
oxygen  is  exhausted,  the  nitrifying  bac- 
teria diminish  in  numbers,  as  they  cannot 
live  without  air,  and  the  efficiency  of  the 
purification  process  diminishes.  If  the  ap- 
plication of  sewage  ceases,  the  beds  grad- 
ually become  drained  as  the  sewage  goes 
down,  air  is  drawn  into  the  pores  of  the 
bed,  until  finally  a  new  supply  is  secured 
and  the  operation  can  be  repeated.  The 
sewage  in  filter  beds  spreads  itself  in  thin 
films  over  the  sand  grains,  thus  giving 
bacteria  an  opportunity  to  develop,  feed 
upon  the  organic  matter,  and  so  break  it 
up  as  to  cause  the  formation  of  new  com- 
pounds, until  the  organic  matter  is  trans- 
formed into  inorganic. 

If  intermittent  filtration  were  a  mere 
straining  process,  then  the  finer  the  sand 
used  the  higher  the  degree  of  purification. 
As  already  pointed  out,  it  is  a  nitrifying 
rather  than  a  straining  process,  so  the  aim 
must  be  to  select  a  material  of  the  size  best 
suited  to  that  end,  and  which  will  at  the 
same  time  give  the  highest  rate  of  filtra- 
tion with  the  least  expenditure  of  labor. 


135 


The  finer  materials  give  a  luw  rate  of  fil- 
tration and  a  high  degree  of  purity.  The 
sewage  not  only  enters  the  sand  slowly, 
but  a  long  time  is  required  to  drain  it  out 
and  renew  the  air.  If  crowded,  poor  re- 
sults and  ultimate  clogging  follow.  With 
coarse  material  the  sewage  passes  through 
too  rapidly  for  nitrification  to  take  place. 
The  drainage  and  air  renewal  can  therefore 
be  effected  quickly.  It  is  thus  evident  that 
with  very  fine  material  the  sewage  must 
be  applied  slowly,  with  long  intervals  of 
rest,  while  with  very  coarse  material  the 
rate  of  application  must  be  yet  slower  and 
the  rests  far  more  frequent,  though  short. 
As  compared  with  material  of  a  medium 
size,  the  fine  does  not  give  sufficiently  bet- 
ter results,  in  actual  practice,  to  warrant 
its  adoption,  nor  does  the  higher  rate  pos- 
sible with  the  coarse  material.  The  slow 
rate  of  filtration  and  the  tendency  to  clog, 
on  the  one  hand,  and  the  very  frequent 
manipulation  of  gates  to  throw  the  beds 
into  and  out  of  use,  on  the  other,  are 
against  the  extremes.  Moreover,  the  very 
coarse  materials  are  not  so  certain  in  their 


136 

removal  of  bacteria  as  fine  ones.  Here,  as 
elsewhere,  a  happy  mean  is  to  be  sought. 
R(  jecting  the  extremes,  the  Massachusetts 
State  Board  of  Health,  in  its  report  for 
1891,  gives  as  the  range  of  available  ma- 
terial sand  having  10  percent,  of  its  weight 
composed  of  grains  finer  than  0.03  to  0.98 
millinuUTS  (0.0012  to  0.0392  ins.). 

All  material  in  filter  sands  finer  than 
O.C1  mm.  (O.C004  ins.)  is  classed  as  organic 
matter.  The  maximum  size  of  the  coarser 
materials  included  in  the  above  range  was 
about  0.5  in.  in  diameter,  and  the  mini- 
mum size  of  the  finest  material  was  0.01  in. 
in  diameter. 

As  the  work  done  by  a  filter  is  largely 
determined  by  smalltr  particles  of  sand, 
and  as  a  sand  of  uniform  size  is  desired,  the 
Massachusetts  State  Board  of  Health  has 
adopted  two  standards  for  comparing  dif- 
ferent materials.  The  sand  is  subjected  to 
mechanical  analysis  to  determine  the  per- 
centages, by  weight,  of  the  total  which 
have  grains  below  a  certain  diameter.  The 
diameter  at  the  10  per  cent,  point  is  taken 
as  the  effective  size,  and  the  uniformity 


137 


coefficient  is  the  ratio  between  the  diameter 
of  the  grains  at  the  60  and  10  per  cent, 
points. 

Although  a  range  in  the  size  of  the  sand 
grains  may  be  allowed,  the  coarse  and 
finer  particles  should  be  fairly  well  inter- 
mingled. Or,  in  other  words,  there  should 
not  be  strata  of  fine  and  coarse  material  in 
a  filter  bed.  The  effect  of  stratification  is 
well  expressed  in  the  report  of  the  Maspa- 
Qhusetts  State  Board  of  Health  for  1892, 
as  follows: 

We  have  thus  found  that  with  a  coarse  material 
above  a  fine  one  in  the  same  filter  thsre  is  a  chance 
of  trouble  from  a  clogging  of  tlio  fine  material  be- 
low the  coarse  ;  and  this  is  far  wo.se  than  surface 
clogging,  for  the  latter  can  be  completely  remedied 
by  disturbing  the  surface  or  by  scraping.  We  have 
also  found  that  a  fine  sand  supported  by  a  coarse 
sand  will  keep  its  lower  layer  saturated  and  act  as  a 
water  seal,  allowing  the  passage  of  water,  but  not 
of  air,  and  may  in  this  way  prevent  tha  necessary 
circulation  of  air,  and  reduce  the  action  of  the  filter 
to  mere  straining. 

*******  * 

The  above  examples  are  perhaps  extreme  cases. 
With  less  marked  differences  in  sand  sizes,  or  with 
gradual  instead  of  abrupt  transitions  from  ccarse 


138 


to  fine,  the  causes  of  failure  might  be  reduced,  or 
even  in  some  cases  entirely  eliminated.  In  the 
many  cases  where  the  fields  available  for  sewage 
filtration  contain  layers  of  various  materials,  the 
different  sands  must  be  separately  studied,  in  order 
to  detormine  the  probabla  action  of  existing  com- 
binations; and  in  case  the  natural  conditiors  are 
unfavorable,  changes  may  be  made  which  will  im- 
prove the  action  of  the  filter. 

Not  all  communities  are  so  fortunate  as 
to  have  ideal  filtering  material  conven- 
iently located  for  sand  filter  beds.  If  net, 
then  the  choice  may  be  between  extending 
the  outfall  sewer  to  a  distance,  with  or 
without  pumping,  and  the  adoption  of  a 
site  giving  poor  material  and  thus  requir- 
ing a  larger  area,  or  an  inferior  sand  may 
be  the  only  kind  available  far  or  near. 
The  Lawrence  experiments,  to  which  ref- 
erence has  freely  been  made,  have  now 
been  carried  on  for  about  seventeen  years, 
and  the  results  of  fifteen  years' studies  of 
a  great  variety  of  material  under  widely 
different  conditions  are  on  record  in  the 
published  reports  of  the  Massachusetts 
State  Board  of  Health.  Actual  results  ob- 
tained at  city  filter  beds  are  also  available, 


139 


so  that  with  expert  advice  any  community 
may  ascertain  the  approximate  possibilities 
of  such  materials  as  are  at  hand.  While 
a  wide  range  of  sands  and  gravels  may  be 
counted  on  for  giving  good  results,  under 
proper  conditions,  it  is  necessary  to  deter- 
mine those  conditions  in  order  to  know 
what  area  of  beds  to  provide,  and  how  to 
apply  the  sewage  after  the  disposal  grounds 
are  ready.  The  area  and  volume  of  sand 
or  gravel  required  for  the  intermittent 
filtration  of  sewage  are  so  large  that  the 
transportation  of  material  any  great  dis- 
tance is  out  of  the  question.  Generally 
speaking,  the  beds  are  constructed  in  ma- 
terial as  naturally  deposited,  top  soil  and 
loam  of  course  being  removed,  together 
with  any  pockets  of  other  unsuitable  ma- 
terial. 

The  sewage  is  carried  to  the  several  beds 
through  open  or  closed  channels  built  in 
the  embankments,  with  distributing  cham- 
bers where  two  or  more  beds  join  together. 
Ordinary  sewer  pipe,  half  pipe,  brick,  con- 
crete or  even  wood  conduits  may  be  used. 
The  distributing  chambers  may  be  of  any 


140 

of  the  above  materials,  excepting  sewer 
pipe,  but  are  generally  of  masonry.  Wood 
carriers  or  accessories  are  to  be  avoided,  if 
possible,  on  account  of  becoming  sewage- 
soaked,  and  thus  liable  to  give  off  bad 
odors. 

The  sewage  should  be  brought  onto  the 
beds  so  as  to  disturb  their  surface  as  little 
as  possible,  and  great  pains  should  be  taken 
to  distribute  it  evenly  over  the  whole  bed. 

The  underdrains  should  rarely,  if  ever, 
be  placed  more  than  50  feet  apart,  and 
should  be  provided  with  manholes,  or 
inspection  chambers  at  all  intersections. 
Underdrains  are  sometimes  put  much 
nearer  together  than  this.  Their  size  and 
depth  will  be  governed  by  the  amount  of 
effluent  they  are  expected  to  remove,  the 
ground  water  level  and  possibly  other  local 
conditions. 

Before  admitting  sewage  to  the  beds  it 
is  generally  advisable  to  screen  it,  at  least 
sufficiently  to  take  out  paper,  rags  and 
large  floating  matter.  The  screening  cham- 
bers often  serve  to  some  extent  as  settling 
tanks,  but  must  be  of  pretty  large  size  to 


141 


remove  any  considerable  proportion  of  the 
total  matters  in  suspension. 

Crops  are  sometimes  raised  on  filter 
beds,  which  is  equivalent  to  practicing 
broad  irrigation  in  summer  and  filtration 
the  remainder  of  the  year.  The  beds  gen- 
erally being  thoroughly  underdrained,  and 
the  soil  often  more  permeable  than  that  of 
a  broad  irrigation  area,  larger  doses  of 
sewage  may  probably  be  applied  to  crops 
on  filter  beds  than  those  growing  on  ordi- 
nary sewage  farms. 

The  size  of  each  bed  should  be  such  as 
to  permit  an  easy  and  equable  distribution 
of  sewage  over  it.  Where  the  total  filtra- 
tion area  is  small  it  must  be  divided  so  as 
to  permit  of  intermittent  operation;  that 
is,  if  a  bed  is  to  be  in  use  and  at  rest  for 
equal  periods,  then  at  least  two  beds  would 
be  necessary,  and  so  on  according  to  the 
relative  periods  of  use  and  rest.  Some 
additional  area  should  also  be  provided 
for  use  while  beds  are  being  scraped  or  in 
case  of  an  emergency.  If  a  large  area  is 
laid  out  so  that  the  size  of  the  beds  is  lim- 


142 

ited  only  by  convenience  in  use,  then  an 
acre  may  be  a  very  acceptable  size. 

As  to  degree  of  purification  which  may 
be  expected,  and  the  rate  of  filtration,  it 
may  be  said,  without  going  into  details, 
that  practically  all  of  the  organic  matter 
may  be  removed  from  sewage  by  inter- 
mittent filtration  at  rates  approximating 
100,000  gallons  per  acre  per  day,  with  the 
best  material  and  all  conditions  favorable. 
With  unfavorable  conditions  the  rate  may 
be  as  low  as  30,000  gallons  per  acre  per 
day  or  even  less. 


CONTACT  BEDS. 

To  make  possible  an  increase  in  the  low 
rates  feasible  with  intermittent  filtration 
under  even  the  best  conditions,  and  also  to 
lessen  the  clogging  of  such  beds  (the  two 
efforts  being  largely  identical),  the  Massa- 
chusetts State  Board  of  Health  early  began 
to  experiment  with  various  preliminary 
processes  of  sewage  treatment,  including 
rapid  filtration  of  various  sorts  and  sedi- 
mentation. A  little  later  than  these  exper- 


143 

iments,  and  in  some  instances  coincident 
with  them,  a  number  of  men  began  exper- 
iments on  their  own  account.  These  in- 
cluded the  late  Colonel  George  E.  Waring 
in  America,  and  Scott-Moncrieff,  Dibdin 
and  others  in  Great  Britain.  In  the  latter 
country  intermittent  filtration  has  almost 
always  been  supplemental  to  broad  irriga- 
tion or  sewage  farming.  The  clayey  na- 
ture of  most  of  the  available  land  and  the 
density  of  population,  made  imperative 
some  change  in  sewage  treatment  in  Great 
Britain,  and  from  about  1892  on  gave  rise 
to  a  multiplicity  of  new  schemes.  Except 
for  details  these  schemes  may  be  narrowed 
down  to  contact  beds  and  percolating  fil- 
ters, with  the  septic  tank,  which  has  been 
described  already,  available  as  preliminary 
to  either  of  these,  and  also  to  broad  irriga- 
tion and  sewage  farming.  Although,  as  a 
rule,  it  is  dangerous  to  credit  these  newer 
processes  to  a  single  man,  the  contact  bed 
may  be  ascribed  to  W.  J.  Dibdin,  for  some 
years  Chemist  to  the  London  County  Coun- 
cil. The  percolating  filter,  as  described  in 
subsequent  pages,  cannot  be  so  readily 


144 

credited  to  a  single  individual,  since  the 
Massachusetts  State  Board  of  Health,  Col- 
onel Waring,  Scott  Honor i off  and  several 
others  had  a  hand  in  its  development. 
Both  the  contact  bed  and  the  percolating 
filter,  in  their  working  form  and  the  extent 
of  their  use,  are  essentially  British.  It 
may  also  be  stated  here  that  the  septic 
tank  was  combined  with  contact  beds  al- 
most if  not  quite  from  the  beginning  of 
the  development  of  the  former  by  Donald 
Cameron. 

The  contact  bed  differs  from  the  Ameri- 
can type  of  intermittent  filter  in  being 
composed  of  much  coarser  material,  gen- 
erally enclosed  by  water-tight  walls  and 
floor,  the  basin  thus  formed  being  pro- 
vided with  inlet  and  outlet  gates.  It  also 
differs  from  the  intermittent  filter  in  that 
when  in  use  the  outlet  gates  are  closed, 
the  bed  filled  quickly  and  held  full  for  two 
hours  or  so,  then  emptied  quickly  and  kept 
empty  for  two  to  four  or  five  hours.  The 
series  of  operations  is  called  a  cycle,  and 
there  are  from  two  to  four  cycles  in  each 
24.hours.  The  filling  and  emptying  gates 


145 


are  frequently  worked  automatically  by 
means  of  specially  designed  apparatus. 

Contact  beds  are  built  -for  operation 
singly,  in  pairs  and  in  groups  of  three; 
the  sewage  in  the  last  two  cases  passing 
through  two  or  three  beds  in  succession. 
When  built  in  pairs  a  coarse  and  a  fine 
bed  are  provided.  The  coarse  material  is 
approximately  from  3-4  to  2  ins.  in  great- 
est diameter,  and  the  fine  material  from 
1-4  to  1  in.  The  material  now  most  com- 
monly used  in  contact  beds  abroad  is  hard 
clinker  from  soft  coal  or  from  refuse  de- 
structors, but  coke,  broken  stonea  gravel 
and  other  substances  may  be  employed. 
Care  should  be  taken  to  select  a  material 
which  does  not  readily  disintegrate.  The 
coarse  beds  are  sometimes  called  primary, 
and  the  fine  ones  secondary,  and  sometimes 
the  terms  single  and  double  contact  beds 
are  used. 

The  relatively  large  size  of  the  material 
composing  these  beds,  and  of  the  intersti- 
tial spaces,  permits  quick  filling  and  emp- 
tying, and  facilitates  also  a  rapid  renewal 
of  the  air  supply  in  the  free  spaces  or  pores 


146 


of  the  bed.  The  latter,  in  turn,  favors  an 
enormous  bacterial  development  and  a  cor- 
lespondingly  speedy  breaking  down  and 
transformation  of  the  organic  matter  of 
the  sewage.  As  can  be  understood,  hold- 
ing the  sewage  in  the  bed  in  contact  with 
the  bacterial  agents  gives  the  beds  their 
name. 

Some  form  of  preliminary  treatment, 
most  commonly  septic  or  sedimentation 
tanks,  has  been  found  advisable  before 
applying  sewage  to  contact  beds,  particu- 
larly where  only  a  single  contact  is  pro- 
vided. A  high  degree  of  bacterial  removal 
is  not  commonly  effected  by  contact  beds, 
unless  very  fine  material  is  employed,  but 
the  organic  matter  in  the  sewage  may  nev- 
ertheless be  so  transformed  as  to  prevent 
nuisance  from  subsequent  putrefaction, 
which  is  usually  the  main  object  of  sewage 
treatment.  With  such  an  object  it  is  re- 
ported that  satisfactory  results  have  been 
obtained  when  passing  settled  or  septic 
sewage  through  double  contact  beds  at 
rates  of  from  500,000  to  ], 000,000  gallons 
an  acre  of  total  surface  area. 


147 

PERCOLATING  FILTERS. 

Trickling,  streaming  and  intermittent 
continuous  filters  are  some  of  the  names 
that  have  been  applied  to  the  last  class  of 
filters  awaiting  consideration,  but  both 
reason  and  usage  are  on  the  side  of  the 
term  percolating  filters. 

The  essential  features  of  percolating 
filters  are  the  use  of  large-sized  material, 
with  the  freest  possible  aeration  and  drain- 
age, and  a  uniform  distribution  of  the 
sewage  over  the  filter  in  drops,  small 
streams  or  spray.  The  sewage  has  an  un- 
interrupted passage  through  the  drainage 
system  of  percolating  filters,  just  as  through 
intermittent  filters,  but  tLe  sewage  is  ap- 
plied continuously,  or  with  numerous  brief 
interruptions  that  break  the  continuity  but 
a  little,  in  the  case  of  percolating  filters, 
and  the  distribution  is  so  even  and  rapid, 
and  the  pores  of  the  filters  are  so  large, 
that  no  sewage  stands  oa  the  percolating 
filters,  whereas  the  surface  of  intermittent 
filters  is  often  flooded  hours  at  a  time. 

Percolating  filters  are  generally  built  on 


148 

a  solid  floor  of  concrete  or  other  water- 
tight material,  and  enclosed  by  open- 
jointed  walls,  the  latter  consisting  of  large 
fragments  of  the  medium,  laid  up  with 
open  joints,  or  regular  sized  moulded  or 
cut  pieces,  laid  pigeon-hole  fashion.  Tne 
body  of  percolating  filters  is  composed  of 
clinker,  stone  or  other  fairly  cohesive  ma- 
terial, in  particles  from  the  size  of  a  hen's 
egg  or  a  man's  fist  up  to  that  of  a  man's 
head,  the  larger  pieces  being  placed  at  the 
bottom. 

Distributors  for  percolating  filters  may 
be  revolving  radial  arms  of  wrought-iron 
pipe,  perforated,  or  revolving  radial  weirs, 
or  fixed  pipes  provided  with  mere  perfora- 
tions or  with  spray  nozzles.  Drains,  formed 
in  the  concrete  or  other  solid  floor,  or  con- 
sisting of  specially  moulded  tiles,  are  used 
to  ensure  thorough  drainage. 

The  effluent  from  percolating  filters, 
even  when  the  original  sewage  is  given  a 
preliminary  treatment,  is  usually  high  in 
finely  divided  suspended  matter,  and  also 
in  bacteria,  but,  as  a  rule,  the  effluent  is 
non-putrefactive  and,  being  largely  min- 


149 

eral  matter,  is  easily  removed  or  reduced 
in  quantity  by  a  brief  period  of  sedimen- 
tation. The  rates  claimed  for  percolating 
filters,  dosed  with  septic  sewage,  range 
from  1,000,000  to  10,000,000  gallons  an 
acre,  but  in  the  present  state  of  the  art 
2,000,000  to  3,000,000  gallons  seems  high. 

SEWAGE     PURIFICATION     PLANTS    NOT 

NUISANCES. 

There  is  often  much  opposition  to  sew- 
age purification  plants  by  those  living  or 
owning  property  near  by  on  the  ground 
that  such  works  must  of  necessity  be  a 
nuisance.  From  experience  gained  by 
visiting  many  such  plants,  both  in  this 
country  and  abroad,  and  from  studying 
the  subject  in  other  ways  for  years,  I  know 
that  well  conducted  plants  are  entirely  in- 
offensive, either  within  or  without  their 
enclosures.  The  employees  about  such 
works  are  as  healthy  as  similar  classes 
of  men  in  other  occupations,  and 
the  same  holds  true  of  the  families  of  these 
men  living  on  the  European  sewage  farms. 


150 


The  crops  raised  on  sewage  farms  are  as 
safe  eating  as  those  of  the  same  kind  rais- 
ed elsewhere.  There  are  objections,  how- 
ever, to  applying  sewage  to  crops  for  hu- 
man consumption  which  are  to  be  eaten 
without  being  cooked,  but  meat  and  milk 
from  sewage  farms  is  usually  as  good  as 
when  produced  under  other  conditions. 

Good  design  and  construction,  followed 
by  proper  methods  of  operation,  are  all 
that  are  needed  to  make  sewage  purifica- 
tion a  success,  when  once  the  right  system 
has  been  adopted  and  put  into  use.  No 
one  system  can  be  said  to  be  the  best  for 
all  localities.  The  special  problems  of 
each  community  must  be  met  and  solved 
case  by  case  and  out  of  several  systems 
and  combinations  of  systems  the  best  for 
the  conditions  at  hand  must  be  chosen. 

THE  PRESENT  STATUS  or  SEWAGE 

PURIFICATION. 

In  the  United  States,  chemical  precipita- 
tion is  no  longer  being  adopted  for  new 
plants.  The  septic  tank  has  come  more 
rapidly  into  favor  than  contact  beds  or 


151 

percolating  filters,  but  some  men  of  prac- 
tical experience  seem  strongly  inclined  to 
plain  sedimentation  rather  than  the  septic 
tank.  Comparatively  few  percolating  fil- 
Uis  have  been  built,  but  small  contact 
beds  are  in  use  in  a  number  of  cases.  In- 
termittent filtration  has  for  years  been  the 
system  most  in  use  in  America,  and  seems 
likely  to  continue  to  lead  where  sandy  land 
for  filter  beds  is  available  at  a  reasonable 
price.  In  our  Far  West,  sewage  irrigation 
is  frequently  practiced,  but  as  a  rule  the 
sewage  is  merely  a  substitute  for  water  in 
sections  where  irrigation  is  a  necessity. 
What  appears  to  be  the  most  successful 
sewage  farm  in  the  United  States  treats 
the  sewage  of  Pasadena,  Cal.  Large  and 
paying  crops  of  walnuts  are  raised  each 
year.  On  a  visit  to  the  Pasadena  sewage 
farm  in  March,  1905,  the  author  was  told 
that  a  large  number  of  orange  trees  would 
be  set  out  soon,  and  that  sewage  would  be 
put  on  these  in  the  summer  and  on  the 
walnut  trees  in  the  winter. 

Early  in  1904  the  author  visited  twenty- 
four  sewage  works  in  Great  Britain  and 


152 


three  on  the  continent  of  Europe.  lie 
found  numerous  chemical  precipitation 
plants  and  sewage  farms  still  in  use,  at 
the  works  visited  and  elsewhere,  but  many 
of  these  were  being  converted  to,  or  sup- 
plemented by,  the  newer  processes.  The 
septic  tank  was  widely  used.  Contact  beds 
were  numerous  and  percolating  filters  were 
fast  becoming  so. 

In  America  the  septic  tank,  contact  beds 
and  percolating  filters  are  far  less  often 
used,  compared  with  other  processes,  than 
in  Great  Britain.  Local  conditions  abroad, 
it  should  be  remembered,  are  widely  dif- 
ferent from  local  conditions  here.  The 
streams  of  Great  Britain  are  small  and  the 
population  dense,  requiring  more  sewage 
works  than  are  yet  felt  to  be  necessary  in 
the  United  States,  and  the  clayey  soil  and 
absence  of  good  natural  filtering  ma- 
terial in  England  and  Scotland  compels 
the  adoption  of  clinker,  coke  and  other 
substitutes.  All  these  things  should  be 
remembered  in  selecting  a  mode  of  treat- 
ment and  filter  bed  material  for  American 
sewage  works. 


153 


If  it  seem  to  any  that  the  newer  pro- 
cesses of  sewage  treatment  have  been  but 
briefly  discussed,  the  author  would  point 
out  the  fact  that  in  1904  there  was  pub- 
lished a  whole  volume  in  this  series,  enti- 
tled, "  The  Treatment  of  Septic  Sewage," 
by  George  W.  Rafter,  M.  Am.  Soc.  C.  E. 
Later  in  1904,  the  author  of  the  book  now 
being  brought  to  a  close,  embodied  his  re- 
cent observations  in  Great  Britain  and  at 
Paris,  Frankfort  and  Wiesbaden,  in  "  Brit- 
ish Sewage  Works."  Present  day  sewage 
treatment,  from  the  viewpoint  of  British 
authorities,  is  set  forth  in  Barwise's  "  The 
Purification  of  Sewage,"  Rideal's  "  Sewage 
and  the  Bacterial  Purification  of  Sewage," 
and  Dibdin's  "The  Purification  of  Sewage 
and  Water."  The  first  American  book  on 
sewage  was  Rafter  and  Baker's  "  Sewage 
Disposal  in  the  United  States,"  a  large 
treatise  on  the  subject  published  early  in 
1894,  before  the  septic  tank,  contact  beds 
and  percolating  filters  had  come  into  pub- 
lic view.  A  revision  of  this  treatise  is 
under  consideration. 


THE   VAN   NOSTRAND   SCIENCE    SERIES 


No.  47.    LINKAGES:    THE  DIFFERENT  FORMS 

and  Uses  of  Articulated  Links.     By  J.  D.  C.  De  Roos. 

No.  48.    THEORY     OF     SOLID     AND     BRACED 

Elastic  Arches.  By  William  Cain,  C.E.  Second  edi- 
tion, revised  and  enlarged. 

No.  49.    MOTION  OF  A  SOLID  IN  A  FLUID.     By 

Thomas  Craig,  Ph.D. 

No.  50.    DWELLING-HOUSES;      THEIR     SANI- 

tary  Conduction  and  Arrangements.  By  Prof.  W.  H. 
Corfield. 

No.  51.    THE  TELESCOPE:    OPTICAL  PRINCI- 

ples  Involved  in  the  Construction  of  Refracting  and 
Reflecting  Telescopes,  with  a  new  chapter  on  the 
Evolution  of  the  Modern  Telescope,  and  a  Bibliography 
to  date.  With  diagrams  and  folding  plates.  By 
Thomas  Nolan.  Second  edition,  revised  and  enlarged. 

No.  52.       IMAGINARY     QUANTITIES;       THEIR 

Geometrical  Interpretation.  Translated  from  the 
French  of  M.  Argand  by  Prof.  A.  S.  Hardy. 

No.  53.   INDUCTION  COILS;   HOW  MADE  AND 

How  Used.     Eleventh  American  edition. 

No.  54.    KINEMATICS     OF     MACHINERY.      By 

Prof.  Alex.  B.  W.  Kennedy.  With  an  Introduction  by 
Prof.  R.  H.  Thurston. 

No.  55.    SEWER  GASES;    THEIR  NATURE  AND 

Origin.  By  A.  de  Varona.  Second  edition,  revised  and 
enlarged. 

*No.  56.  THE  ACTUAL  LATERAL  PRESSURE 

of  Earthwork.     By  Benj.  Baker,  M.  Inst.,  C.E. 

No.  57.      INCANDESCENT    ELECTRIC    LIGHT- 

ing.  A  Practical  Description  of  the  Edison  System. 
By  L.  H.  Latimer.  To  which  is  added  the  Design  and 
Operation  of  the  Incandescent  Stations,  by  C.  J.  Field; 
and  the  Maximum  Efficiency  of  Incandescent  Lamps, 
by  John  W.  Howell. 

No.  58.    VENTILATION   OF  COAL  MINES.     By 

W.  Fairley,  M.E.,  and  Geo.  J.  Andre. 

No.  59.    RAILROAD  ECONOMICS;    OR,  NOTES 

With  Comments.     By  S.  W.  Robinson,  C.E. 

No.  60.     STRENGTH        OF        WROUGHT-IRON 

Bridge  Members.     By  S.  W.  Robinson,  C.E. 
No.  61.    POTABLE  WATER,  AND  METHODS  OF 

Detecting  Impurities.      By  M.  N.  Baker.     Second  edi- 
tion, revised  and  enlarged. 
No.  62.     THEORY   OF   THE    GAS-ENGINE.      By 

Dougald  Clerk.  Third  edition.  With  additional 
matter.  Edited  by  F.  E.  Well,  M.E. 


THE   VAN   NOSTRAND   SCIENCE    SERIES 

No.  63.     HOUSE-DRAINAGE     AND     SANITARY 

Plumbing.     By  W.  P.  Gerhard.     Twelfth  edition. 

No.  64.    ELECTROMAGNETS.      By  A.  N.  Mans- 
field.    Second  edition,  revised. 

No.  65.     POCKET      LOGARITHMS      TO      FOUR 

Places  of  Decimals.  Including  Logarithms  of  Num- 
bers, etc. 

No.  66.    DYNAMO-ELECTRIC  MACHINERY.   By 

S.  P.  Thompson.  With  an  Introduction  by  F.  L.  Pope. 
Third  edition,  revised. 

No.  67.    HYDRAULIC  TABLES  FOR  THE   CAL- 

culation  of  the  Discharge  through  Sewers,  Pipes,  and 
Conduits.  Based  on  "Kutter's  Formula."  By  P.  J. 
Flynn. 

No.  68.     STEAM-HEATING.     By   Robert   Br 

Third  edition,  revised,  with  additions  by  A.  R.  W 

No.  69.   CHEMICAL  PROBLEMS.     By  Prof.  J.  C. 

Foye.     Fifth  edition,  revised  and  enlarged. 

No.  70.    EXPLOSIVE       MATERIALS.     By    Lieut. 

John  P.  Wisser. 

No.  71.     DYNAMIC       ELECTRICITY.     By    John 

Hopkinson,  J.  N.  Shoolbred,  and  R.  E.  Day. 
No.  72.     TOPOGRAPHICAL       SURVEYING.      By 

George  J.  Specht,  Prof.  A.  S.  Hardy,' John  B.  McMaster, 

and  H.  F.  Walling.     Fourth  edition,  revised. 
No.  73.    SYMBOLIC  ALGEBRA ;    OR,  THE  ALGE- 

bra  of  Algebraic  Numbers.     By  Prof.  William  Cain. 
No.  74.    TESTING     MACHINES;      THEIR    HIS- 

tory,  Construction  and  Use.     By  Arthur  V.  Abbott. 
No.  75.    RECENT     PROGRESS     IN     DYNAMO- 

electric  Machines.     Being  a  Supplement  to  "Dynamo- 
electric  Machinery.     By  Prof.  Sylvanus  P.  Thompson. 
No.  76.    MODERN    REPRODUCTIVE    GRAPHIC 

Processes.      By  Lieut.  James  S.  Pettit,  U.S.A. 
No.  77.    STADIA     SURVEYING.     The  Theory  of 

Stadia    Measurements.     By   Arthur   Winslow.     Eighth 

edition. 
No.  78.    THE      STEAM  -  ENGINE      INDICATOR 

and  Its  Use.     By  W.  B.  Le  Van. 
No.  79.      THE    FIGURE    OF    THE    EARTH.     By 

Frank  C.  Roberts,  C.E. 
No.  80.    HEALTHY          FOUNDATIONS  FOR 

Houses.     By  Glenn  Brown. 
*No.  81.    WATER      METERS:       COMPARATIVE 

Tests  of  Accuracy,  Delivery,  etc.     Distinctive  Features 

of    the    Worthington,    Kennedy,    Siemens,    and    Hesse 

meters.     By  Ross  E.  Browne. 


THE   VAN   NOSTRAND   SCIENCE    SERIES 


No.  82.    THE  PRESERVATION  OF  TIMBER  BY 

the  Use  of  Antiseptics.  By  Samuel  Bagster  Boulton, 
C.E. 

No.  83.    MECHANICAL      INTEGRATORS.         By 

Prof.  Henry  S.  H.  Shaw,  C.E. 

No.  84.  FLOW    OF    WATER    IN    OPEN    CHAN- 

nels,  Pipes,  Conduits,  Sewers,  etc.  With  Tables.  By 
P.  J.  Flynn,  C.E. 

No.  85.   THE      LUMINIFEROUS      AETHER.      By 

Prof.  De  Volson  Wood. 

No.  86.    HANDBOOK    OF    MINERALOGY;     DE- 

termination,  Description,  and  Classification  of  Minerals 
Found  in  the  United  States.  By  Prof.  J.  C.  Foye. 
Fifth  edition,  revised. 

No.  87.    TREATISE  ON  THE  THEORY  OF  THE 

Construction  of  Helicoidal  Oblique  Arches.  By  John 
L.  Culley,  C.E. 

*No.  88.  BEAMS  AND  GIRDERS.  Practical  For- 
mulas for  their  Resistance.  By  P.  H.  Philbrick. 

No.  89.   MODERN  GUN  COTTON:    ITS  MANU- 

facturo,  Properties,  and  Analyses.  By  Lieut.  John  P. 
Wisser,  U.S.A. 

No.  90.  ROTARY  MOTION  AS  APPLD3D  TO 
the  Gyroscope.  By  Major  J.  G.  Barnard. 

No.  91.  LEVELING:  BAROMETRIC,  TRIGONO- 
metric,  and  Spirit.  By  Prof.  I.  O.  Baker.  Third 
edition. 

No.  92.  PETROLEUM;  ITS  PRODUCTION  AND 
Use.  By  Boverton  Redwood,  F.I.C.,  F.C.S. 

No.  93.  RECENT  PRACTICE  IN  THE  SANI- 
tary  Drainage  of  Buildings.  With  Memoranda  on  the 
Cost  of  Plumbing  Work.  Second  edition,  revised  and 
enlarged.  By  William  Paul  Gerhard,  C.E. 

No.  94.  THE  TREATMENT  OF  SEWAGE.  By 
Dr.  C.  Meymott  Tidy. 

No.  95.  PLATE-GmDER  CONSTRUCTION.  By 
Isami  Hiroi,  C.E.  Fourth  edition,  revised. 

No.  96.  ALTERNATE-CURRENT  MACHINERY. 
By  Gisbet  Kapp,  Assoc.  M.  Inst.,  C.E. 

No.  97.  THE  DISPOSAL  OF  HOUSEHOLD 
Wastes.  Second  edition.  By  W.  Paul  Gerhard,  Sani- 
tary Engineer. 

No.  98.  PRACTICAL  DYNAMO-BLTLDING  FOR 
Amateurs.  How  to  Wind  for  Any  Output.  By  Fred- 
erick Walker.  Fully  illustrated.  Third  edition. 

No.  99.  TRIPLE-EXPANSION  ENGINES  AND 
Engine  Trials.  By  Prof.  Osborne  Reynolds.  Edited 
with  notes,  etc.,  by  F.  E.  Idell,  M.E. 


THE   VAN   NOSTRAND   SCIENCE    SERIES 


No.  100.   HOW  TO  BECOME  AN  ENGINEER;   or, 

The  Theoretical  and  Practical  Training  necessary  in 
Fitting  for  the  Duties  of  the.  Civil  Engineer.  By  Prof. 
Geo.  W.  Plympton. 

No.  101.  THE      SEXTANT,   and   Other  Reflecting 

Mathematical  Instruments.  With  Practical  Hints  for 
their  Adjustment  and  Use.  By  F.  R.  Brainard,  U.  S. 

Navy. 

No.  102.   THE     GALVANIC     CIRCUIT    INVESTI- 

gated  Mathematically.  By  Dr.  G.  S.  Ohm,  Berlin, 
1827.  Translated  by  William  Francis.  With  Preface 
and  Notes  by  the  Editor,  Thomas  D.  Lockwood. 
M.I.E.E.  Second  edition. 

No.  103.  THE  MICROSCOPICAL  EXAMINATION 

of  Potable  Water.  With  Diagrams.  By  Geo.  W. 
Rafter.  Second  edition. 

No.  104.   VAN  NOSTRAND'S  TABLE-BOOK  FOR 

Civil  and  Mechanical  Engineers.  Compiled  by  Prof. 
Geo.  W.  Plympton. 

No.  105.     DETERMINANTS.     An  Introduction   to 

the  Study  of,  with  Examples  and  Applications.  By 
Prof.  G.  A.  'Miller. 

No.  106.   COMPRESSED  AIR.     Experiments  upon 

the  Transmission  of  Power  by  Compressed  Air  in  Paris. 
(Popp's  System.)  By  Prof.  A.  B.  W.- Kennedy.  The 
Transmission  and  Distribution  of  Power  from  Central 
Stations  by  Compressed  Air.  By  Prof.  W.  C.  Unwin. 
Edited  by  F.  E.  Idell.  Third  edition. 

No.  107.   A  GRAPHICAL  METHOD  FOR  SWING 

Bridges.  A  Rational  and  Easy  Graphical  Analysis  of 
the  Stresses  in  Ordinary  Swing  Bridges.  With  an  Intro- 
duction on  the  General  Theory  of  Graphical  Statics,  with 
Folding  Plates.  Second  edition.  By  Benjamin  F.  La 
Rue. 

No.  108.   SLIDE-VALVE    DIAGRAMS.      A    French 

Method  for  Constructing  Slide-valve  Diagrams.  By 
Lloyd  Bankson,  B.S.,  Assistant  Naval  Constructor, 
U.  S.  Navy.  8  Folding  Plates. 

No.  109.   THE    MEASUREMENT    OF   ELECTRIC 

Currents.  Electrical  Measuring  Instruments.  By 
James  Swinburne.  Meters  for  Electrical  Energy.  By 
C.  H.  Wordingham.  Edited,  with  Preface,  by  T.  Com- 
merford  Martin.  With  Folding  Plate  and  Numerous 
Illustrations. 

No.  11O.  TRANSITION     CURVES.     A  Field-book 

for  Engineers,  Containing  Rules  and  Tables  for  Laying 
out  Transition  Curves.  By  Walter  G.  Fox,  C.E. 
Second  edition. 


THE   VAN   NOSTRAND  SCIENCE    SERIES 


No.  111.   GAS-LIGHTING     AND     GAS-FITTING. 

Specifications  and  Rules  for  Gas-piping.  Notes  on  the 
Advantages  of  Gas  for.  Cooking  and  Heating,  and 
Useful  Hints  to  Gas  Consumers.  Third  edition.  By 
Wm.  Paul  Gerhard,  C.E. 

No.  112.   A   PRIMER   ON   THE    CALCULUS.      By 

E.  Sherman  Gould,  M.  Am.  Soc.  C.E.     Third  edition, 
revised  and  enlarged. 

No.  113.  PHYSICAL  PROBLEMS  and  Their  So- 
lution. By  A.  Bourgougnon,  formerly  Assistant  at 
Bellevue  Hospital.  Second  edition. 

No.  114.   USE       OF      THE       SLIDE      RULE.      By 

F.  A.  Halsey,  of  the  "American  Machinist."     Fourth 
edition,  revised  and  enlarged. 

No.  115.  TRAVERSE  TABLE.  Showing  the  Dif- 
ference of  Latitude  and  Departure  for  Distances  Between 
1  and  100  and  for  Angles  to  Quarter  Degrees  Between  1 
Degree  and  90  Degrees.  (Reprinted  from  Scribner's 
Pocket  Table  Book.)  Third  edition. 

No.  116.  WORM  AND  SPIRAL  GEARING.  Re- 
printed from  "American  Machinist."  By  F.  A.  Halsey. 
Second  revised  and  enlarged  edition. 

No.  117.   PRACTICAL      HYDROSTATICS,      AND 

Hydrostatic  Formulas.  With  Numerous  Illustrative 
Figures  and  Numerical  Examples.  By  E.  Sherman 
Gould. 

No.  118.   TREATMENT    OF    SEPTIC     SEWAGE, 

with  Diagrams  and  Figures.  By  Geo.  W.  Rafter.  Second 
edition. 

No.  119.  LAY-OUT  OF  CORLISS  VALVE  GEARS. 

With  Folding  Plates  and  Diagrams.  By  Sanford  A. 
Moss,  M.S.,  Ph.D.  Reprinted  from  "The  American 
Machinist,"  with  revisions  and  additions.  Second 
edition. 

No.  120.   ART  OF  GENERATING  GEAR  TEETH. 

By  Howard  A.  Coombs.  With  Figures,  Diagrams  and 
Folding  Plates.  Reprinted  from  the  "American  Ma- 
chinist." 

No.  121.  ELEMENTS     OF     GAS     ENGINE     DE- 

sign.  Reprint  of  a  Set  of  Notes  accompanying  a  Course 
of  Lectures  delivered  at  Cornell  University  in  1902.  By 
Sanford  A.  Moss.  Illustrated. 

No.  122.   SHAFT    GOVERNORS.      By    W.    Trinks 

and  C.  Housum.      Illustrated. 
No.  123.  FURNACE  DRAFT ;    ITS  PRODUCTION 

by  Mechanical  Methods.  A  Handy  Reference  Book, 
with  figures  and  tables.  By  William  Wallace  Christie. 
Illustrated.  Second  edition,  revised. 


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